What major event led many to be sympathetic with the Jews and caused many Jews to return to Palestine?

The major event in question was World War II.

Explanation:

During World War II, many people groups sufered great losses because of fascist politics, and the group of people that suffered the greatest losses in percentage of the total population were the Jews. It was Nazi Germany that started off and motivated other countries to eliminate the Jewish population, and some of the other countries involved in this were Italy, Hungary, Lithuania, and Bulgaria.

The estimates are that around 6 million Jews lost their lives because of the genocide over them. After the war ended, the majority of the countries in the world felt very sympathetic with the Jews and agreed that they deserve their own country after what they experienced. This new country was supposed to be located in the historical homeland of the Jewish people, Israel. The area was inhabited mostly by a Muslim Arab population, with the minority being represented by Jews, but this rapidly changed as millions of Jews flocked in, and since they had the international support they created their own country, which unfortunately led to conflict.

a. european colonies