I think you've gotten some great advice so far.
I just wanted to throw in my perspective "from the other side." I'm American and came to live in Holland with my Dutch DH. Should be easy, right? I don't look different from the majority Dutch culture (well . .. I'm short and plump and Dutch women tend to be tall and skinny, but anyway . . . . I'm caucasian and, majority Dutch culture is too), most Dutch people speak excellent English, culturally it is relatively close to North America . ... WRONG!!!
I suffered *major* culture shock. Now . .. .after *nine* years in Holland, I finally feel at home and have made a great life for myself. However, I *still* have days when everything drives me crazy, I'm super-homesick, and I think Holland is just a dismal, water-logged little nation full of rude, small-minded people!
(my DH is Dutch, as I said and my DS is half-Dutch . .. really . .. I love them . . .. .)
My point, OP, is not to discourage you! It's just to say that even when cultures are relatively similar like Holland and North America, it can take a long time to adjust to things. You probably know that from having lived in Kenya yourself. But I do think there is a difference between moving somewhere for work/school/adventure with the knowledge that it's an adventure and you can and will leave whenever you want (not sure if that was your situation or not in Kenya?) and moving somewhere to be with your partner semi-permanently.
Before I met DH, I had traveled all over the world and had lived for extended periods of time in both Brazil and Israel. I never suffered the culture shock I did in Holland, an arguably far more comparable culture to North America. Why? Not sure, but I think it was because when I moved to Holland, I was there *for* DH and to build a whole life there and that was overwhelming and discouraging, at times. In Brazil and Israel, I was there to work and for the adventure and experience and knew I could pull up stakes and leave whenever I wanted.
OP, I would just keep encouraging your DH to make friends but not push him. It can take a while. Also, please try not to take "attacks" on American culture personally. When I'm having a bad day, in general, everything in Holland is awful (see above) and everything in America is perfect. Of course, I know rationally that isn't true. I know it isn't true when I'm saying it. But sometimes it is so frustrating to be "the outsider" and just not be completely in control by knowing all the social "rules" and it can be overwhelming. Keep on building your life and, hopefully, your DH will eventually follow.
Hang in there!