Prior to Israel's War of Independence in 1948, the Jews of Palestine urged Arab inhabitants to remain in the area and become part of the nascent state. Despite these pleas, however, the majority of Arabs fled, many heeding their own leaders' promises that they could return after the Jews were driven into the sea.
Israel's declaration of establishment explicitly called on the Palestinian Arabs to participate in building the state and pledged equal rights for all, regardless of religion or ethnicity. This promise was fulfilled for the 150,000 Arabs who remained and became Israeli citizens.
The rest of the Arab population left Israel and settled as refugees in the surrounding Arab states of Lebanon, Syria, Jordan (including the West Bank) and Egypt (including the Gaza Strip). Despite billions of dollars in international aid and an entire organization created solely to oversee the Palestinian refugees - the United Nations Relief & Works Agency - the number of Palestinian refugees continue to swell even to this day. These neighboring Arab countries, for their part, made a tactical decision long ago to not build the refugees any permanent housing or allow them to integrate into society, preferring instead to keep them in camps as political pawns and as symbols of Arab suffering.
Today, there are nearly 5 million Palestinian refugees. In the interest of peace, Israeli leaders have repeatedly expressed a willingness to absorb some of these refugees and the state has already accepted nearly 200,000 of them; however, the Arabs refuse to negotiate over the supposed "right of return" and made clear they consider the refugee issue a weapon in their continued war against Israel.
Israel's acceptance of a "right of return" would amount to national suicide.
As the corresponding map shows, the return of every refugee would swell Israel's population to more than 12 million while in the process making Arabs the majority.
The world's only Jewish state would cease to exist.