In 1948, after the founding of Israel, a coalition of Arab countries attacked the new state. During the conflict, many Arabs left their homes in what was now Israel. Most were urged to evacuate by Arab leaders, who anticipated a swift return after the expected defeat of Israel. Others were forcibly removed as part of the war effort. (We will admit to this.)
This led to the displacement of approximately 750,000 Palestinian Arabs.
Around 150,000 Arabs remained in Israel and became citizens. Today, there are about 2 million Israeli Arab citizens.
In comparison, over 900,000 Jews were expelled or fled from Muslim-majority countries in the Middle East and North Africa during the same period.
Other significant refugee crises in the 20th century include: 1.5 million people displaced between Turkey and Greece in the 1920s; 14-18 million displaced during the partition of India in 1947; about 12 million Germans after World War II; and 2-3 million displaced by the Korean War.