It is by no means clear that militarism is actually a good thing for the United States. There are many people, in fact, who would say that it is a bad thing. If, however, we have to assume that militarism is a good thing, we can say that it makes the United States more important in the world and it helps make us wealthier and more patriotic.
Militarism can be defined as the idea that we should have a strong military and that we should be prepared to use it aggressively to defend or promote our interests in the world. We can argue that militarism helps us in the world by making us more of a power. When we have a strong military and other countries can see that we are willing to use it, those other countries will be afraid of us. They will be more likely to go along with what we want. This is good for our country.
On the home front, militarism is also good for us. Militarism improves our economy because our government spends a lot of money on military equipment. Moreover, as the government tries to get better military equipment, new technologies are developed. These new technologies eventually help our civilian economy as we find peaceful applications for them. Just as importantly, militarism makes us more cohesive and more patriotic. When we have militarism, we are more likely to respect our troops and to support our country. We are less likely to be critical of our country and its aims. When our citizens support our country vigorously, we are better-off as a society.
In these ways, (we can argue) militarism improves our standing in the world, our economy, and the cohesiveness of our society.