The 1948 war. Dunno why that wasn't clear for you from context.

Who started it is an interesting question. Obviously, both sides didn't plan to abide by the UN resolution.

“The acceptance of partition does not commit us to renounce Transjordan; one does not demand from anybody to give up his vision. We shall accept a state in the boundaries fixed today. But the boundaries of Zionist aspirations are the concern of the Jewish people and no external factor will be able to limit them.” David Ben-Gurion, in 1936, quoted in Noam Chomsky, “The Fateful Triangle.”

The consequences that should have followed were keeping the UN's borders and allowing the repatriation of the people driven out under Plan Dalet. That's the difference between a defensive war and a war of conquest.