It takes a lot less money and knowledge to tear things down than it does to build them up. Especially if the members are willing to die for the cause.
Not much is needed actually: men (people), weapon of some kind, and charisma the rest falls in place.
These countries you’re thinking of are usually attacked regularly where survival is an everyday struggle. For people who dedicate their everyday to survival; it’s only expected that they would be fighting back.
In terms of funding…a lot of rich people would love to take advantage of people in this kind of situation. You could also easily make the argument that these rich people help cultivate this kind of situation for their own benefit as well.
I understand it’s very similar to how people get wrapped up in a cult.
Charismatic leadership/ideology and exerting top-down control in much the same way cults operate.
Terrorism is actually a pretty simple but specific definition. Terrorists use unlawful violence and threats of violence to influence the government or an international governmental organisation, or to intimidate the public. They do this in pursuit of a political, religious, racial or ideological cause.
It doesn’t take much money or many resources to engage in violence or even make threats. Certainly having money and resources at your disposal make you more effective but it’s a rather low but still specific bar to cross to be considered a terrorist.
It’s not terribly difficult to find recipes for explosives online. Take up a collection among like-minded people to purchase supplies, rent a vehicle, and park it in the garage of a target. Low-effort terrorism.
Some things take a lot of time and knowledge, but budget-terrorism also exists.