The phenomenon of Jews returning to Israel did not start after World War II, it began hundreds of years earlier.
After the collapse of the Crusader kingdoms in the 13th century, Jews started returning to Israel. The driving force behind this migration was the growing anti-Jewish agitation on the European continent.
One of the most destructive flare-ups of anti-Jewish hatred in medieval Europe was the Great Bonfire of Paris where thousands of Jewish books were burned.
Following the disputation of Paris, a great debate was organized in Spain between Pablo Christiani, a Jewish convert to Catholicism and Rabbi Moshe Ben Nachman a renowned Jewish scholar. The Disputation of Barcelona was held in the year 1263. Following this event Rabbi Nachman was forced to leave Spain. He moved to Jerusalem and founded a Yeshiva.