Since 1948 there have been five wars between Israel and its Arab neighbors.
--1948 Independence War.
--1956 Suez War
--1967 Six Day War.
--1967-1970 Attrition War.
--1973 Yom Kippur War.
All the wars were started by Arabs.
All the wars were won by Israel.
The conflict goes back far earlier with Jews claiming that the land of Israel is theirs by right in line with a promise made in the Hebrew bible. Muslims also claim rights to the land in line with the Qur'an. The validity of those claims has been debated for more than a millennium and there has been no consensus reached so far.
It is this long running conflict that has been the root of the five wars of 1948, 1956, 1967, 1967-1970 and 1973. The politics of the region are remarkably complex with opinions polarized across the world. Each war was triggered by events relating to the long held claims to the land. The more difficult question of who was responsible for the wars will garner very different answers from those involved and like the issue of rights to the land, these questions are still being debated.
Each of the different Arab-Israeli Wars started for a different reason. The Arab-Israeli Conflict also has it genesis in a complex set of events. Look at the Related Questions below for more information.