The world had seen many protests and deaths and violence and US kept quiet..... Sudan Somalia Nepal & even Myanmar when monks marched.

Why they will appear to be intervening is actually a very simple logic. They will pretend to be doing it when they found out that power change already become inevitable - e.g. during Suharto's fall. They do it for several purposes:

1. To create false impression that the USA was powerful that under their intervention 3rd world regimes changed hands.

2. They hurry in to buy some friendship with the new regime by doing some redundant assistance.

3. The US need to stay on the GOOD side of the books of new 3rd world powers.

4. When there are several possible alternative powers that could replace a falling regime, the USA will then try to see if they can help the one faction that is most friendly with Washington to gain power. But they will do that if the cost is not too high to Washington.

When change is into the hands of those hostile against USA, they will wash hands and run ASAP. USA is a lame bullshit, they will not want lose their lives and limbs and look for only very cheapo wins.....doesn't anybody?