Catherine II of Russia prided herself on being called 'emperor', not 'empress'. Having dumped her weak husband, she deployed her lovers strategically: one she made king of Poland, one she sent to conquer Crimea, and one to rule over it. Here are the origins of Russia's claims to Ukraine.

Dr Kelly O'Neill, an historian of Russia at Harvard University, and the author of Claiming Crimea: A History of Catherine the Great's Southern Empire, joins Beatrice and Paul for this episode.

Coming from an aristocratic family of the Holy Roman Empire, Catherine II married the heir to the Russian imperial throne, but upon his accession, managed to seize power and reigned in her own right from 1762-1796. She plunged into European great power politics with great talent and sweeping strategic moves. Previously, Russia had not had access to the Black Sea and the Mediterranean trade beckoning beyond it. Catherine even had her eye on Constantinople, and dreamed of freeing it from Turkish occupation to restore it to Christendom under the rule of her grandson, fittingly named Constantine. While this did not come to pass, by the end of her reign, Russia had occupied a large part of the Polish Lithuanian empire, dominated the Black Sea and was a European great power. It was said that no cannon in Europe could be fired without her leave, a line that Russian Foreign Minister Sergei Lavrov currently likes to use in his speeches: clearly, his master would like to restore this situation.

The Swedish campaigns in Central Europe in the Thirty Years' War are remembered in folklore for their brutality, for massacres of civilians and 'scorched earth' tactics. And yet, as their leader, King Gustavus II Adolphus of Sweden (1594 – 1632) is remembered almost as a saint, even in these very same regions.

King Gustavus Adolphus, an experienced military commander who had already fought and won wars against the Polish-Lithuanian Commonwealth and Denmark, intervened in the Thirty Years' War like a force of nature – a 'Lion from Midnight'. He was the champion of the Protestant cause, fighting the Catholic Habsburgs and their followers. In a series of huge moves, his armies swept through the Holy Roman Empire, winning battles at Frankfurt/Oder, Werben, Breitenfeld, Rain on the River Lech, and, finally, Lützen – but this last Swedish victory cost him his life.

Professor Gunnar Åselius explains the paradox: Gustavus Adolphus prided himself on his military reforms and the discipline he kept among his soldiers, but even they would turn to pillage and murder to feed themselves when they were not paid. Holding degrees from the universities of Uppsala and Stockholm, Professor Åselius teaches Military History at the Swedish Defence University.

Julius Caesar is famous for describing hugely complicated strategic problems, then adding his famous Vini, vidi, vici: 'I came, I saw, I conquered'. But what did his strategic genius consist of? And how did he justify extending the Roman Empire right across Western Europe?

Did Rome acquire her empire, not quite in a fit of absent-mindedness, but defensively, or was she ruthlessly expansionist? Gaius Iulius Caesar's account of his Gallic Wars (58-50 BC) explained his military operations as 'just' wars: Rome came to the rescue of allies and quelled lawless rebels. Admittedly, Caesar showed outstanding generalship. Forced marches by Roman infantry, operations - even in winter - caught adversaries by surprise. Complementing kinetic tools of siege craft and battle, Caesar's diplomacy turned Gallic and Germanic tribes and their leaders against each other, forging alliances and isolating adversaries, just as he had done previously in Roman domestic politics.

Dr Louis Rawlings helps us dissect Caesar as a strategist and as a political animal. Rawlings holds his degrees from University College London, having previously taught there and at the Department of War Studies, King's College London. He is now Senior Lecturer in Ancient History at Cardiff University.

While most of the political and military commanders whom we now call 'great' were often ruthless or megalomaniacs, Korean Admiral Yi Sun-sin is remembered not only for his military prowess but also for his integrity and humility. He came to his nation's rescue in extremis when others had failed.

The 15th and 16th century saw unprecedented creativity in naval warfare. The Chinese, Portuguese, Spanish, English, Japanese and Koreans each employed their first blue water navies in distinct ways, for distinct strategic purposes, and with distinct technological innovations. In 1592, Admiral Yi Sun-sin answered the call to rescue his country from invasion, despite having been undeservedly court-martialled twice and reduced to the ranks by hostile superiors who were jealous of his abilities. Vastly overmatched, with only a dozen innovative 'turtle ships' and some support from Chinese naval forces, he defeated the Japanese fleet, isolating the Hideyoshi army and ending the Imjin War – a triumph that cost him his life.

Lt Cdr Dr Seok Yeong-dal teaches naval history and strategy at the Republic of Korea Naval Academy. His PhD from Yonsei University in Seoul examined the successes and limitations of the Royal Navy's reforms in the 19th century. He has written extensively on Admiral Yi, as well as on the Royal Navy in the 19th century with his recent book, A Failed Reform or The First Steps of Reforms, Achievements and Limitations of the Royal Navy's Reforms in the 19th Century, published in South Korea in 2023.

Frederick II of Prussia, like the Era of the Enlightenment in which he lived, was torn about warfare: was it to be humanised, or was it to be perfected? As king he favoured the latter, earning the respect of contemporaries as the greatest strategist of his age.

Frederick in his youth thought Machiavelli's instructions for princes morally reprehensible, and as a king surrounded himself with great moral philosophers, including, famously, Voltaire. But Frederick saw it as his duty, as that of any monarch, to increase the territorial possessions of his dynasty, even by war, irrespective of just causes. One of the last monarchs who was his own commander-in-chief on his military campaigns, he was also a crafty political strategist, wresting Silesia away from Empress Maria Theresia yet persuading her to colluding with him (and Catherine II of Russia) in the partition of Poland.

Dr Adam Storring helps us understand this complicated man, who like Xerxes and Alexander III before him, was obsessed with outdoing and outshining his father. A Cambridge man, Dr Storring was awarded the André Corvisier Prize for the worldwide Best Dissertation on Military History in 2019. His publications include works on Frederick the Great, including in the forthcoming Cambridge History of Strategy (2024). He teaches at the Department of War Studies, King's College London.

Alexander III of Macedon posed as the 'Son of Zeus', but followed the advice of his biological father, King Philip II, to get out of Macedon and "seek a kingdom equal to yourself". Between 336 and 323 BC, Alexander the Great created the largest empire the Middle East had known.

Macedonian expansionism had begun under Philip II, with his son Alexander II picking up and honing the armed forces created by his father. But where Philip's strategic aims were to dominate all of Greece and Western Asia Minor, Alexander's sight was set on bringing the Persian Empire to heel. And as he moved from sieges and massacres to battle after victorious battle, his ambitions grew further – the conquest of Afghanistan and India. How did he keep his Macedonian and Greek companions motivated? Without him to lead, they did not know how to get back?

Dr Andrew Fear, Lecturer in Ancient History at the University of Manchester, joins Paul and Beatrice to tell us about the strategies of Alexander. An Oxonian, he has a spate of publications on Alexander and on warfare in Antiquity, with contributions to the Cambridge History of Greek and Roman Warfare (CUP 2007) and to the forthcoming Cambridge History of Strategy, co-edited by Beatrice, and Isabelle Duyvesteyn. He is co-editor with Dr Jamie Wood of A Companion to Isidore of Seville (Brill, 2015).

Shaka Zulu (c. 1787–1828) was the most powerful king in southern Africa during the pre-colonial period. He forged a polity that would become the largest in the region through the ruthless use of his reorganised and loyal army.

Initially regarded as an upstart, Shaka managed to impose himself as a regional ruler. Invaded by a powerful neighbouring tribe, he organised the collective defence of the Zulus and other tribes, reorganising the militia and drawing on indigenous traditions, without any European influences. He then turned to crushing the surrounding chiefdoms with the utmost brutality, leaving a trail of massacres and destruction in his wake. Operating with only 5,000 to 10,000 warriors at any given time, Shaka – like Napoleon – prevailed not through the introduction of new technologies, but through innovative ways of training and employing his army.

Professor John Laband is the world-leading expert on Zulu history. A graduate of the University of Natal and Cambridge, he is Professor Emeritus of History at Wilfrid Laurier University, Canada. He joins Beatrice and Paul for this episode.

Dr John O. Hyland joins Paul and Beatrice to discuss fifth-century BC Persian ruler Xerxes I, whose royal progress took him to the Western boundaries of his empire.

Xerxes I tried to extend his rule beyond the Aegean, which his father had failed to accomplish. For a land power this was a challenge, despite the formidable army that Xerxes commanded. He used two strategic tools – engineering, to construct a pontoon bridge across the Hellespont, and the hire of a navy, to tackle the Athenian fleet. While the latter did not work so well for him at Salamis, Xerxes' army returned by land.Safely back beyond the Straits, Xerxes portrayed himself as conqueror and enforcer of order on the Greeks.

Dr John O. Hyland is the perfect specialist to talk to us about Xerxes, and also about the theory of a Greek or 'Western' Way of War, identified and scorned by Xerxes' cousin Mardonius, and contrasted with a supposedly more subtle 'Eastern' way of war. Dr Hyland holds a PhD on the Ancient Mediterranean World from the University of Chicago and teaches at Christopher Newport University. His next book will explore Persia's Greek Campaigns.

The credit for successful military campaigns often goes to the senior commander, when in fact, the brilliance of the operation and the planning happened at much lower levels of the organisation. This is the case with Subotai (1175 – 1248), Genghis Khan's leading general.

Veteran and military historian Dr Angelo Caravaggio joins Paul and Beatrice to discuss Subotai, the brains behind Genghis Khan's vision of conquest, and the one who should be in receipt of many of the strategic credits given to Khan. Many of the concepts that we talk about today at military colleges about strategy and tactics – speed, manoeuvre, surprise, the deep battle, the battle of annihilation, even the concept of Mission Command – were all practiced by the Mongols under Subotai. Without Subotai, the Mongols would not have defeated Korea, China, Poland, Persia, Russia or Hungary. This does not, however, make him a hero to worship; he had the majority of the population of Afghanistan killed, the entire population of towns that would not yield were massacred, in one case right down to the cats and dogs.

Dr Angelo developed a keen interest in Subotai and holds his degrees from the Royal Military College of Canada and the Wilfrid Laurier University. He has been teaching at the Canadian Forces College for 13 years, specialising in leadership, defence and security.

To conclude Season Three of Talking Strategy, US Army General (ret.) Dr David Petraeus shares with us his philosophy about making good strategy. A scholarly soldier with a long and varied career, he commanded the International Security Assistance Force in Afghanistan in 2010–11 and subsequently served as director of the CIA.

General Petraeus's experience has taught him that the best results can arise from what he describes as his own 'intellectual construct for strategic leadership', comprised of four tasks: brainstorming, communication, implementation and assessment. Successful results can be achieved from initially brainstorming with the best and brightest around the commander to find the next 'big idea' – thinking through all good proposals, and deciding which is the best. Then, the challenge is to communicate it to the entire defence establishment both at home and abroad, including one's own forces and allied/coalition forces. Then comes the implementation, requiring energetic leadership. Finally, the results must be assessed – and here the circle closes.

For General Petraeus, making and implementing good strategy is possible when the armed forces are turned into a learning organisation, one that can draw lessons and jettison approaches that have been unhelpful. For communication with multiple audiences during an armed conflict, his motto is: 'Be first with the truth'.