See How the U.S. and Iran Cycle Between War and Cease-Fire

After weeks of all-out war, the United States and Iran agreed to a two-week cease-fire in April that paved the way for more negotiations and held open the possibility of a lasting peace.

Just days later, clashes started again over control of the Strait of Hormuz, a crucial route in the global oil trade. After the United States blockaded Iranian ports, Iran attacked vessels and declared it was closing the waterway.

Seesaws between fighting and calm are common in peace processes, said Laura Wise, a research fellow at the University of Edinburgh. As proposals from warring parties vie with counterproposals, some cease-fire violations are only to be expected.

What is happening in this war is another matter.

“The level of volatility, and how public the whiplash back and forth has been — that’s not normal,” Ms. Wise said. The process has been further complicated, she said, by an American government that seems focused on “getting a deal rather than making peace.”

Tensions continued to rise in May. After the United States began using military ships to escort vessels through the strait, Iran launched more attacks on vessels. The U.S. military responded with force.

In mid-June, Iran and the United States announced that an agreement had been reached. The countries signed a memorandum of understanding to cease hostilities for the next 60 days, and the United States lifted its naval blockade.

The truce would not last.

The vague language of the deal led to even more disagreement over who controlled the Strait of Hormuz, through which ships transited freely before the war.

Clashes resumed in late June after the United States accused Iran of another attack on a commercial vessel.

Days later, the United States and Iran once again agreed to halt fighting in the strait. The lull soon ended. After Iran targeted more ships, Mr. Trump declared the cease-fire over on July 8 and began a round of attacks that would bring the countries back to the brink of all-out war.

After two weeks of intensive U.S. bombing in southern Iran, the war once again appeared on pause for several days, with neither country acknowledging any direct strikes or counterstrikes over the weekend but both sides threatening to resume the fighting. That came to pass in the early hours of Wednesday morning, when the United States and Saudi Arabia targeted Iranian proxies in Iraq, and the Iranian military said it had attacked U.S. military assets in Jordan.