That is when Israel declared independence?
Were the Jews hungry for land and started kicking Arabs out, or did the Arabs attack first, or is it sort of a mixed bag?
In 1948, the Arabs attacked first. A few hours after Israel became an independent country, most of the Arab countries of the region invaded.
But that's just the 1948 answer.
Local Arab and Jewish militia forces had been clashing for years. A few months earlier (in 1947) bombings and shootings had increased to the level of a civil war. Jews were being driven out of their homes throughout the Arab world, then the Arabs were fleeing their homes in Israel during the '48 war. Whose fault it all was depends entirely on who you ask.