The size of the demonstrations Friday shows how attached Palestinians remain to the “right of return”—the notion that Palestinian refugees and their millions of descendants should be allowed to return to the homes their families had in what is now Israel. Palestinians say this is a key condition in any negotiations with Israel over a future state. The Israelis view this as a nonstarter, saying it is unrealistic for Palestinians, many of whom have only lived in refugee camps in places like Lebanon, to come to a country their ancestors left—a return that could irreversibly alter the demographic makeup, and by extension the Jewish nature, of the state of Israel. Indeed, a massive Palestinian march along the border with Israel could arguably trigger Israeli fears about Palestinians marching on Israel and overwhelming it demographically.

The protests also coincide with a significant religious period for both Jews and many Christians: Passover, when Jews celebrate their ancestors’ liberation from slavery in ancient Egypt, begins Friday. It is also Good Friday, which falls in the middle of the Christian holy week that culminates in Easter. Palestinian protests during this period add to the tensions in a region that isn’t a stranger to them.

Relations between Israel and the Palestinians have been fraught for decades. The optimism of the 1990s that followed the signing of the Oslo Accords between the two sides have given way to mutual mistrust and violence. Waves of Palestinian suicide bombings and rocket attacks frayed Israeli nerves; Israeli military retaliation was often swift. Israel’s construction of a barrier along its border with the West Bank saw a marked reduction in the number of Palestinians who crossed into Israel to carry out attacks. Israel disengaged from Gaza in 2005, but kept control over its airspace and territorial waters. Blockaded by Israel, Gaza became virtually cut off from the rest of the world. Hamas won elections there in 2006. Israel, as well as the United States, regards Hamas as a terrorist organization—and refuses to deal with it directly.

Western attempts at mediation are moribund, much like the peace process between the two sides. Last year, Fatah, the Palestinian faction that governs the West Bank, signed an agreement on a unity government with Hamas, its rival. Past attempts at such a government have been unsuccessful. Israel says it will not deal with any unity government that includes Hamas. Still, the Trump administration is said to be on the verge of releasing its peace plan, formulated by Jared Kushner, the president’s son in law, and some advisers. But the fact that Trump broke with decades of U.S. precedent and international diplomacy by announcing his intention to move the U.S. Embassy to Jerusalem from Tel Aviv means that any Palestinian buy-in for such a plan is dead on arrival.