You should probably read these articles:

Hamas launched in 1988 in Gaza at the time of the first intifada, or uprising, with a charter now infamous for its anti-Semitism and its refusal to accept the existence of the Israeli state. But for more than a decade prior, Israeli authorities actively enabled its rise. At the time, Israel's main enemy was the late Yasser Arafat's Fatah party, which formed the heart of the Palestinian Liberation Organization (PLO). Fatah was secular and cast in the mold of other revolutionary, leftist guerrilla movements waging insurgencies elsewhere in the world during the Cold War. ... The Israelis saw [the Muslim Brotherhood's] adherents in the Palestinian territories, including the wheelchair-bound Sheik Ahmed Yassin, as a useful counterweight to Arafat's PLO. ... "When I look back at the chain of events I think we made a mistake," one Israeli official who had worked in Gaza in the 1980s said in a 2009 interview with the Wall Street Journal's Andrew Higgins. "But at the time nobody thought about the possible results."

https://www.washingtonpost.com/news/worldviews/wp/2014/07/30/how-israel-helped-create-hamas/

“Hamas, to my great regret, is Israel’s creation,” Avner Cohen, a former Israeli religious affairs official who worked in Gaza for more than two decades, told the Wall Street Journal in 2009. Back in the mid-1980s, Cohen even wrote an official report to his superiors warning them not to play divide-and-rule in the Occupied Territories, by backing Palestinian Islamists against Palestinian secularists. “I … suggest focusing our efforts on finding ways to break up this monster before this reality jumps in our face,” he wrote.

https://theintercept.com/2018/02/19/hamas-israel-palestine-conflict/

You think Palestinian unity was gonna fix the problems with Israel?

Divide and conquer. Divide and rule.

Old as time and proven track record.