A materialist explanation for why the US has an inferior military, despite being more expensive, is that the US military is driven by profit for the capitalist class. The excess cost is stolen by the capitalists.

Here is a section of the letter which is more about historical materialism. It talks about how the US extracts resources from underdeveloped countries, which leads people from those countries to migrate to the US, and then the US uses violence against those migrants.

The ignorance of American leaders leads to a cascade of problems—a vicious cycle creating a whirlpool of catastrophe. They spend billions of dollars interfering in and destabilizing independent countries—countries that wish to preserve their self-autonomy and national values—to plunder their natural resources. As a result, a flood of homeless people from those countries pours into the United States. Then they spend billions more to control illegal immigration and return immigrants to their countries. The plundered riches end up in the pockets of the elite, while all the costs of this vicious cycle are borne by the American taxpayers.

Driven by the ambition to dominate the world economy, they put in place policies to facilitate economic globalization without considering the long-term consequences. They sing the praises of free trade and rant against the evils of tariffs. Then, after two decades, when they realize that the United States has lost great swathes of its manufacturing landscape to developing countries, they once again shift gears abruptly and—again without considering the long-term consequences—go into knee-jerk-reaction mode and start indiscriminately smacking tariffs on all sorts of countries, making matters even worse. And it’s the American people who are left holding the bag.

The same ignorance is evident in how the U.S. pulled out of its international environmental commitments to allow the government more leeway to pursue growth in the hope that it could boost its manufacturing sector. Then, when they have to deal with the costs of mitigating the consequences of pollution, they again lay all the economic burden at the feet of the American taxpayers. The rich keep getting richer, and the poor poorer. It’s the American taxpayers that always pay the price of their leaders’ incompetence. The leaders themselves are never held accountable.