In the war between Israel and the Palestinian group Hamas, each side’s most powerful ally has aligned behind it. To support Israel, the US moved additional warships, aircraft and troops into the Middle East and expedited shipments of munitions. Iran, which backs Hamas, has said that Israel’s military operation against the group would be answered by the anti-Israeli and anti-Western groups it supports — the so-called axis of resistance. Already, the war between Israel and Hamas, considered a terrorist group by the US and European Union, has stoked violence in other parts of the Middle East and raised concerns of a wider conflagration. These are some areas of concern:

After Hamas militants massacred 1,200 people in Israel on Oct. 7 and set off the war, the Lebanese militia Hezbollah began launching missile, mortar and rocket strikes on northern Israel in solidarity with Hamas. Cross-border fire between Israel and Hezbollah — which is influenced heavily by Iran’s elite Islamic Revolutionary Guard Corps — has become a daily occurrence, threatening to open a second front of the war. Both Hamas and Hezbollah receive funding, weapons and training from Iran. Hezbollah has a bigger, more professional fighting force than Hamas and, Israeli authorities estimate, almost 10 times the number of missiles. Israel and Hezbollah have fought repeated battles, including a war in 2006.