The current conflict between Israelis and Palestinians stemmed directly from recent history, most notably, the Zionist movement and Balfour Declaration, which was a,pledge by the British that supported the establishment of a Jewish state. Once this was declared, masses of people started emigrating to the area now known as Israel. Naturally, this caused conflict, since Palestinians resented and feared the emigration of so many foreigners to what they considered their homeland. Things went from bad to worse when Israel was finally given statehood, which Arab states refused to acknowledged, causing a war that Israel eventually won, and which laid the groundwork for the conflict you see today.
All of this has absolutely nothing to do with the Crusades, which happened a millennium ago and involved a battle between Christians and Muslims over the Holy Land.
The origin of the Israel and Palestinian conflict goes back about a hundred years, and the cultural group referred to as Palestinians didn't truly coalesce until the 1960s. During Crusader times, Muslims were actually far better to Jews than Christians, and when the Christians captured Jerusalem they killed both with impunity.
I do not believe the original Crusades into the Holy Land formed much of the contemporary issues between the Israelis and Palestinians. These clashes were happening before the Crusades, Europe merely played into it and made it worse for a number of years. Clashes in the area were happening prior to Jesus's time even.
Desert Islam and Muhammad's family started issues with Jews and Israelis around 632 when the Muslim faith began. Crusades a few hundred years later exacerbated tensions in the Holy Land, but the original issues of land held by Jews and Muslims still existed. Hopefully, both sides will learn to get along and not blow each other up over settlements and resources.
The original Crusaders into the Holy Land did not form much of the contemporary issues between Israelis and Palestinians, because the issues existed before the Crusades. It was long foretold in the Bible that there would always be conflict in the area. He predicted it when Jacob and Esau were born. The conflict continues today.