About Afghanistan, I dont think leaving was a mistake. It was something that had to be done and should probably have been done 10-15 years ago to be frank. The problem was with how it was executed. Before Trump left office he invited the Taliban leaders to the US and sat down with them and negotiated an american withdrawal. The plan was that the US would exit Afghanistan during the winter 2020-2021 by first removing the soft targets and expensive installations and then gradually removing the fighting forces and retreating towards Kabul. This withdrawal was supposed to have been finished in may 2021.
Problem was that as soon as Trump lost (or "lost") the election the generals in Pentagon who opposed leaving Afghanistan canceled these plans. And when Biden entered office he officially canceled the plans. May 2021 came an went and when the Talibans saw that the Americans had not followed through on their promise they went on the offensive. In the summer and Biden got the choice of either withdrawing or sending in even more troops to squash this attack. He chose withdrawing.
The execution however was awful. Trump had chosen to withdraw in winter because Afghanistan is pretty much all mountains that will be full of snow or be flooded in the winter. This makes it very hard to move for the Talibans, but not so much on the Americans that have heavy vehicles and choppers. So it would have been safer. The second problem was that Biden removed soldiers and security forces first and just left their equipment and civilian people behind.
The third big problem was that the Americans did not realize how popular the Talibans were with the common population in Afghanistan. The normal government had no support from its soldiers and was seen as completely corrupt. Thus despite the fact that the government forces outnumbered the Taliban 300k to 75k. (On paper) Most soldiers just turned over their weapons or even joined the Talibans when they came. Thus the Talibans could conquer the entire country in two weeks without ever fighting a battle.
You might not like it, but this is democracy in action!
I think most cells in the region are funded through iran or turkey.
Al qaeda was supposedly funded by saudis. But that may have been a cover story. Saudi arabia lacks history / motive for funding terrorism.
Me being american, take what I say here with a grain of salt.
Wait? What! You do realize that 16 out of 21 the 9/11 hijackers were Saudis right? And that Osama Bin Laden himself was a Saudi? Also, Saudi Arabia was one of the primary sponsors of IS in Syria (Other significant sponsors includes the USA and Israel. At least before they realized that maybe IS were bad people.)
The only reason that america did not invade Saudi Arabia instead of Afghanistan was that the saudi princes were buddy buddy with the Bush and Clinton families as well as other deep state creeps and thats how they escaped the terror label.