(CNN) — After three difficult years, armed groups loyal to Tehran appear to be bouncing back across the Middle East, reinforcing Iran’s leverage in its war with the United States and Israel.

For decades, experts say, these groups played a key role: acting as a powerful deterrent against direct attacks on Iran. The “Axis of Resistance” – an anti-Israel and anti-Western alliance of regional militias backed by the Islamic Republic – was, however, significantly weakened by Israel’s large-scale military response to the 2023 Hamas attack and the regional repercussions that followed.

It was when this axis was in a weakened state that direct conflict between Israel, the US and Iran erupted. Today, however, several armed groups allied with Tehran are back to pressuring Iran’s foes by opening new fronts that complicate the war and threaten to choke the global economy.

“The Axis (of Resistance) worked very well for more than two decades, helping ensure there was no attack on Iran while these groups extended their influence within their own territories,” Trita Parsi, executive vice president of Quincy Institute for Responsible Statecraft, told CNN. “Once they were weakened, Iran paid the price by having both the US and Israel attack it.”

Iran’s reaction to this was not to abandon the forward defense, but to reinvest in it, Parsi said.

Tehran has long pursued a pan-revolutionary strategy, exporting the values born of its 1979 revolution to neighboring countries and territories, including Lebanon, Yemen, Iraq, Syria and Gaza.

After the 2023 Hamas attack, Israel embarked on a decapitation campaign against several Iranian allies, killing – among others – Hamas leader Yahya Sinwar, one of the masterminds of the October 7 raid, and Hassan Nasrallah, a Hezbollah leader with huge influence in the Middle East.

It also ramped up its attacks on Iran-backed militias in Iraq and exchanged fire with Yemen’s Houthis. Israel even went after Tehran’s own leaders – killing former Supreme Leader Ayatollah Ali Khamenei – in the hope of triggering regime change, which has so far failed.

Three years later, and after a full-blown war, Tehran’s regional allies once again appear to be active, adjusting to the new battlefield landscape in a way that is significantly boosting Iran, experts say.

The Axis of Resistance is “still alive,” said Danny Citrinowicz, former head of the Iran branch of Israeli military intelligence. “It is not disappearing, but it is changing,” he told CNN.