ISIS, or the Islamic State, or ISIL, is the richest terrorist organization in the world (Syria and Iraq). The second richest is Hamas (Gaza Strip), then FARC (Colombia), then Hezbollah (Lebanon), then the Taliban (Afghanistan), then Al-Qaeda (Saudi Arabia), then Lashkar e Taiba (India, Pakistan), then Al-Shabaab (Somalia), then IRA (Ireland), and finally Boko Haram (Nigeria).
As you can see there are 8 Islamist and only 2 socialists terrorist organization in terrorism’s top 10 i.e. IRA and FARC. Oil is obviously the reason Islamists are doing better than socialists. I guess drugs is the reason FARC is doing so well in Columbia. Actually Colombia is also producing and exporting oil so it is difficult to say how FARC pays its bills.
“The World’s 10 Richest Terrorist Organizations”, December 2014