As someone who has lived in the US for 20 years but has moved quite a bit within the country, and lived in multiple other countries before, but continues to travel a lot, I've become very aware of the "stuff" I have. And it's fairly obvious to me that the 2 largest drivers for the stuff have been:

1. Marketing 2. Needing to fill space

I believe most Americans live in far too large houses and would benefit from downsizing, especially once the kids move out. Additionally, I think Americans would benefit from some strategies to avoid impulse buying (the ones I have used successfully in the past, but have lacked the discipline to maintain include never buying anything the day I think of buying it, but always waiting at least 1 day, and avoiding using credit cards and almost entirely depending on cash).