When Hamas terrorists led a deadly attack across the border on Oct. 7, 2023, started a war with Israel that destroyed Gaza. He also set off an extraordinary wave that has reshaped the Middle East in unexpected ways.

Power contracts were suspended. Long established “red lines” were crossed. Years of tyranny at the center of the region were swept away.

Fifteen months after the October attacks, and the cease-fire agreement between Israel and Hamas starting on Sunday, here is a look at how the region has changed dramatically.

Israel

Israel has reasserted its military might but may face significant diplomatic and domestic costs.

The country’s leaders saw the insurgency led by Hamas as an existential threat and were determined to defeat Hamas and weaken its main sponsor, Iran. Israel not only succeeded in weakening Hamas in Gaza, but also defeated the Lebanese Shiite group Hezbollah and seriously defeated Iran’s alliance with the Middle East.

Closer to home, and in the minds of people around the world, Israel’s success has been incomprehensible. Although their attack on Gaza has weakened Hamas significantly, it has not destroyed it, as the government has vowed to do.

Israel’s economy has been crippled by the war, and the country’s politics – which were briefly ignored when the war began – seem to have returned to their predicament. The country is in danger, threatening its diplomatic goals, such as establishing good relations with Saudi Arabia.

That could also change with Monday’s opening for President-elect Donald J. Trump, who pushed in his first term to forge an agreement between the Arab world and Israel and may resume those efforts.

In the long run, it is difficult to describe what Israel will experience from the young Lebanese and Palestinians who are traumatized by the death and destruction that Israeli bombardment has caused to their families and homes.

Hamas

Hamas and its leader at the time of the Oct. 7, Yahya Sinwar, wanted to start a major war between Israel and the allies of Hamas. But the group failed to anticipate the outcome of the conflict.

For ordinary Palestinians, the future looks worse than ever.

Israeli bombings and attacks have forced nearly all Gazans from their homes and killed more than 45,000 people, according to Gazan health officials, who do not distinguish between civilians and combatants. The land of Israel has become a great wasteland.

Israel has killed Mr. Sinwar and all the other Hamas soldiers, and the group’s popularity among Gazans is gone, even by US officials. compare that Hamas has taken almost as many fighters as it has lost in 15 months of fighting.

And yet, its remaining leaders would call its survival a victory.

Israel insists Hamas will not be able to control the city after the war, but it has refused to call for plans for Gaza after the war. Gulf countries like Saudi Arabia now say they will not change their relationship with Israel unless they take a step towards establishing a Palestinian state.

Lebanon

The fractured Hezbollah, once the crown jewel of Iran’s so-called axis of resistance, has unleashed its influence in Lebanon. But Israeli attacks and bombings have left Lebanon facing billions of dollars in rebuilding from its pre-war economic crisis.

Hezbollah, the former political and military force in Lebanon, has faced many challenges since it launched an attack in 2023. Israel has killed many of its leaders, including Hassan Nasrallah. His guardian Iran is weak. And its supply chain through Syria is in jeopardy. To a large extent, the group’s main promise to Lebanon – that it alone could defend the country from Israel – has been canceled.

The years of political turmoil, which blames the terrorist group, rose enough this month for Lebanon’s parliament to elect a new president and appoint a prime minister backed by the United States and Saudi Arabia.

Despite the attack, Hezbollah can still call on thousands of fighters, and has support from Lebanon’s main Shiite Muslim community. It may still find a way to rebuild within Lebanon’s thriving political system.

Syria

The overthrow of Bashar al-Assad last month – one of the most dramatic and unexpected results of the Oct. 7 – ended the brutal dictatorship. But the inevitable chaos that followed created the conditions for a new power struggle.

For almost 13 years, Mr. al-Assad has led an insurgency against his family’s 50 years in power – supported by Russia, Hezbollah and Iran.

But as Moscow focused its war on Ukraine, and Iran and Hezbollah withdrew from Israel, the Turkish-backed Islamist group Hayat Tahrir al-Sham saw an opportunity. He marched through Syria and overthrew the government within days.

With Iran and Russia in the background, Turkey is now in the best position to play a major role in Syria. Moscow hopes to keep some of its naval and air bases, but the future of its talks with Hayat Tahrir al-Sham is unclear.

Meanwhile, the United States has maintained a small force in Syria to fight Islamic State militants and is allied with Kurdish-led forces that Turkey views as an enemy. And Israel has seized the Syrian territory near the Golan Heights as a safe haven and has been carrying out numerous airstrikes against what it says are Syrian military weapons.

Syria’s neighbors and European countries – which host millions of Syrian refugees – are watching closely to see if the country can stabilize or if it will plunge back into violent chaos.

Iran

Iran’s powerful regional alliance has collapsed, leaving the country vulnerable — and encouraged — to develop nuclear weapons.

Seen as one of the strongest powers in the Middle East, Iran has been slow to reform over the past 15 months. It has lost much of its once-powerful “struggle base,” a group of allies it used to counter the influence of the United States and Israel.

Its close ally, Hezbollah, is now too weak to attack Israel. And with Mr. al-Assad removed from Syria, Iran has lost control over a country that provided a critical line of weapons and terrorists.

Previous red lines that prevented the region from world war have been removed: Starting with Israel killed the political leader of Hamas, Ismail Haniyeh, while he was a guest in Tehran, Iran and Israel have made direct threats against each other.

While in reality what leaves Tehran is unknown. A weakened Iranian government that it sees as increasingly vulnerable could be forced to use its decades-old nuclear arsenal. US officials have warned that Iran could only need weeks to enrich enough uranium for a bomb.