I'm assuming these are booked on one ticket so you'll not have to worry about collecting and rechecking baggage or anything like that.
Ninety minutes is plenty to change in Amsterdam. Even with the current renovation it's still pretty easy to get from one gate to another. Since you're going non-EU to non-EU you'll not need to go through passport control but will probably go through a security screening. There's a question here about transiting in 50 minutes which you'll see isn't a problem. If your incoming flight arrives late and you have less time then you'll be allowed to use the 'fast lane' at security (but I think security might be at the gate for that flight -- although this may not be true anymore). I've done hour changes in Amsterdam several times and normally have enough time to stop for a (quick) drink and a snack and still get to the gate in plenty of time. If you don't have an on-going boarding pass you'll need to stop at a transfer desk but these have automated kiosks and are pretty easy to use.
I can't find official minimum connection times for MSP, this FlyerTalk thread says 1 hour for International to Domestic. Since it's your first point of entry to the US you will need to clear immigration and customs at MSP. In general this is just a matter of following the signs picking up your bags if you have checked bags and rechecking them after customs. Since you're a US citizen, you should have no issue with it and the system is pretty well streamlined now.
I'm guessing you're flying Delta or KLM, the in-flight entertainment system has airport guides and transfer tips -- as does their official magazine. They should also tell you the departure gate of the next flight, if they know it, just before landing. If your flights are late you can talk to the cabin crew who should be able to assist you, if you miss a connection your airline should rebook you on a later flight and pay for food / accommodation as required.
If you have high enough frequent flyer status then look out for the signposted lanes that you can use to use which will have shorter queues. If you want to buy more time consider sitting near the front of the plane so your more likely to get off before the bulk of the passengers and then they'll not be ahead of you in the various queues.
That's all assuming it's booked on a single ticket and your bags are checked all the way through. If that's not the case you'll need to collect and recheck your bags at each stop (also going through customs and immigration). If everything went smoothly ninety minutes is maybe enough time to do that but I'd strongly advise you to change the flights to give yourself more time.