Moses Mendelssohn had already acknowledged that Jews in the modern era can make choices about how to practice and believe in Judaism, or whether to keep it at all. A range of choices then emerged in response to this new freedom, including ultra-Orthodoxy, the neo-Orthodoxy of Samson Raphael Hirsch, Reform Judaism, and the emergence of Conservative Judaism with Zacharias Frankel, when he said “yes” to both history and halakhah.

Further reading:
Zachariah Frankel in Mendes-Flohr and Reinharz, The Jew in the Modern World (2nd ed., 1995), 194-197, 178-182.