On gradually and suddenly – The Economist:

‘Iran has been diminished gradually, then suddenly. Back in 2015, it had signed a nuclear deal with the United States and enjoyed broad regional reach. Since then, it has wobbled. In 2018 President Donald Trump tightened sanctions, which sent the economy spiralling downwards. In 2020, America assassinated Qassem Suleimani, Iran’s top general, in Iraq. Iran tried but failed to avoid being dragged into Israel’s war with Hamas following the group’s attack on Israel on October 7th 2023. Just over a year later, its three regional proxies have been destroyed.’

(…)

‘The Islamic Revolutionary Guard Corps (irgc) is trying to put a brave face on the collapse of an alliance that dates back to the dawn of Iran’s revolution. Mr Assad, say its generals, had grown increasingly unreliable and duplicitous as he floundered for allies to save him. Iran and Hizbullah had sent their forces to save him from an earlier uprising in 2013, but he did nothing to reciprocate when Israel attacked their positions in Syria, killing 19 Iranian commanders over the past year. Some suspected him of collusion with Israel.’

(…)

‘For all that, Mr Khamenei is in no imminent danger of suffering Mr Assad’s fate. His regime remains far more functional than Mr Assad’s was. After the suppression of a mass uprising two years ago, most Iranians are too exhausted for another attempt. But they are certainly beginning to question the regime’s strength.’

Read the article here.

I do think that there was an understanding between Assad and Israel. Israel let Assad live, in return Israel could attack Iranian positions with impunity.

As to the Iranian regime, gradually might turn into suddenly there as well.