I disagree with those who are fretting about the 1:40 connection at IAH. 1:40 should be plenty of time at IAH if your inbound flight is on time. If you're Global Entry/PreCheck, like I am, it's even easier.

In the unfortunate event that you misconnect, if you are on a single UA ticket all the way through from AMS-IAH-LAX, you will be protected by UA. There are several later flights from IAH-LAX that could serve as backstops if things go awry.

At IAH, you will clear immigration, pick up your checked bags at the baggage carousel, clear customs, drop your checked bags at the baggage re-check belts to your right just after you walk outside customs, and then you can decide to turn right, take the escalator upstairs, and join most of the coming-off-an-international connecting passengers at the TSA queue or walk through the Terminal E exit, take the escalator or elevator up, and join the regular Terminal E departures TSA checkpoint. The latter option is almost always faster.