2. President Trump told Middle East leaders he would recognize Jerusalem as the capital of Israel, a move that upends decades of U.S. policy, upsets peace efforts between Israel and the Palestinians and threatens to ignite unrest.

It is Mr. Trump’s riskiest decision in the realm of Middle East diplomacy, and Arab and European leaders had warned against it. For now, the U.S. Embassy will stay in Tel Aviv while logistics are worked out.

We talked to top experts and delved into our photo archives for this article about the history of Jerusalem, and why it’s such a flash point. Above, the Dome of the Rock at the Aqsa Mosque compound.