Complex sentence: Ramsey and Keynes cooperated to try to bring Wittgenstein back to Cambridge (he had been a student there before World War I), which made Ramsey to become Wittgenstein's supervisor and the latter to submit the Tractatus Logico-Philosophicus as his doctoral thesis.
Split into simpler sentences: Ramsey and Keynes cooperated to try to bring Wittgenstein back to Cambridge (he had been a student there before World War I). Ramsey became Wittgenstein's supervisor and the latter to submitted the Tractatus Logico-Philosophicus as his doctoral thesis.