How does ISIS do what they do?

Here's my question: All these insurgents, militants, extremists, terrorists, freedom fighters—call them what you will—where do they get such modern weapons, uniforms, ammunition, and military equipment from? Where do they recruit from? How do they train? How are they financed? Does not one catch on till they actually run a city or country over?

I know this may sound as naive as the question about "With all this technology, how could you lose an entire airliner?”, but truth be told, I am more than a bit intrigued about how someone can grow to be so big without a lot of help from someone already big, and how someone already big helping someone become a problem can escape detection from other someones already big too?

And I am not talking of straight lines that could, at one time, be drawn between the two sides of the iron curtain, or about Arab states at war with each other, with both sides being supplied with American arms and training, or about a fringe group overpowering an armoury or a small military depot and having some limited firepower to harass the supply lines of a great colonial power.

I am talking in the 21st century, with the kinds of checks and balances, banking norms, logistical embargos, satellite spying et al. How is it possible to take on American trained Iraqi troops, with American weapons, and defeat them unless you have something equivalent or superior. Obviously, it cannot be equipment or training. but even if we were to put it down to other intangibles, it still takes a very well drilled, well supplied, well-financed, well trained, well-armed, and focused group under an able commander with a continuous and well-protected lines of supply of fresh recruits, training grounds, ammunition, and other logistics (I mean everything, including uniforms, food, water, medicine, fuel, and more) and excellent intelligence to take over a city like Mosul this way. where do they find this without anyone else knowing?