Because of the latest conflicts between USA and Iran, is there any way a WW3 can start? And in what case a ww3 can start?
Honestly, I don't believe this but I want other people's opinion.
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Almost certainly not because Iran doesn't have any state allies in the region (besides Iraq maybe). Even if the US were to invade or even nuke Iran, it will still be a limited regional conflict, even if Iran strikes at Israel or Dubai as they have threatened they might do. Iraq attacked Israel with Scuds during the first Gulf war, but this didn't widen the conflict significantly. That war saw a fairly broad coalition against Iraq, including NATO and [Sunni] Arab countries, yet I don't know anyone calling it a "world war". (Actually, after a fair bit of googling, I did find one paper calling it that; but it's decades old and only has ~10 citations or so. By that standard, we'd be at WW4 or 5 should a war with Iran erupt...)
Iran has the ability to call upon their proxy militias in states like Iraq, Lebanon, Yemen, Syria, etc. But these militias have limited capabilities and are already engaged in various local conflicts. So, worst case, we might see "Gulf War 3", to use a more apt name.
In response to comment regarding Russia: Their interests may align in some respects, particularly Syria, but Russia's military involvement in Iran seems was short lived to the 2016 brief use of the Hamedan airbase, which elicited opposition in Iran as well (and I don't mean on the streets, this was in the Iranian parliament).
Likewise Russia has sold some S-300 anti-air missiles to Iran, but even on this the relationship was less than smooth, with Medvedev banning the sale in 2010, only for it to be revived in 2015. Russia is probably the main foreign weapon supplier to Iran nowadays, but one should not read too much into this. There's no defense treaty between Russia and Iran etc. So yeah, they may have condemned the US attack on Soleimani, but that doesn't meat they'll "stick their necks out" for Iran much.