Actually the causes are neither immigration, nor tariffs. It's garbage monetary policy combined with governmental spending on welfare crap. This is what lead to all the empire collapses(or most).

Tariffs actually decrease economic performance. Just think of it this way. Costs would be a lot higher if the stuff would be produced in the US without a technological advantage, which would lead to people actually living worse. I'm not going to explain this because it's a long thing, but you can research on it. Tariffs were proven to be bad.

Immigration isn't a problem as long as you don't have a huge welfare state because then you'd have more people leeching on the system. Otherwise people would just move there and lower both wages and prices. People think that business wants small wages for people, which is false because it needs people to afford the crap they make. Otherwise they'd be out of business.

The problem is when people reach government dependence. You can look at the Romans for this too. The slippery slops of handouts. Once you start giving them and more and more people get them, you reach a point where you can't stop giving them, which leads to bankruptcy. Look at the US government. Social Security, Medicare and Medicaid have 55 trillion of unfunded obligations. And from government dependence, you get to tyranny.