Well, you can look at things from a cellular level up.
This entire planet, and everything on it.... is trying to kill us, and everything around it. Single cell organisms rape and destroy other cells, impregnating and repurposing those cells to do their bidding. Plant life grows in specific manners and distributes its progeny in order to outgrow/kill off the surrounding plant life, ensuring its species' survival. Animals hunt and eat each other, some killing for pure fun at times with the sole "rule" being "not our own". Then you have the humans, which have a multifaceted approach of being able to wreak the same devastation that everything else can but on a scale that otherwise dwarfs the capacity of the creatures below us on the food chain.... other than bacteria/viruses.
Natures "harmony" we so love to embrace is that plants feed off the carcasses and shits from the kills from the predators who hunted the herbavores which ate the plants. Violence is life on this planet, and people think that they can control it when they're surrounded by it.
Embracing the necessity of action at times, necessity of readiness, and necessity of restraint, as a coupled triad of violent reality.. is something that is necessary. I would love nothing more than for everyone to reliably get along and that I would never need to use any of my weapons in defensive anger at some point.... unfortunately, I'm a realist and there's daily news articles highlighting reasons I need to carry, I need to train, and I need to be prepared. Hopefully a combination of aggressive non-violent action through situational awareness, pre-planning for contingencies, and otherwise being proactive for awareness/acknowledgement/action against what might be/is a threat will prove effective. Unfortunately, that's not always the case and so a solid hand is required in order to ensure that life's wonderful card game is played in my favor, regardless of the flop so to speak.
As to progression of combat capability? I think that we'll remain at the forefront of that. I think that a large portion of world policing, specifically tuning and molding the world (where peaceful neighbors can focus more on growth rather than destruction and therefore benefit us as positive and capable partners in trade) can be accomplished through a cohesive and structured foreign policy that might actually end up costing less than the current status quo of "they don't like us too much, let's throw some money at them" which more often than not either retains someone that the local population dislikes (therefore harboring resentment as a nation other than command)... or retains a two-faced fuckstick and his cronie cooperative in power which is happy to take said cash while fully (and sometimes openly) planning to sink a shiv into our neck when the situation to do so presents itself.
Focusing on convincing the leadership of a nation to do the right thing and having them head in the most adventageous direction with the least amount of dislike towards us, is honestly one of the best ways to work. Even if it means that we just maintain an embassy and otherwise don't do a ton of anything with them. Use the classic "democratic mantra" of "never let a good catastrophe go to waste" and be fully prepared to step in and provide aid at THAT point when they most need it. Heads of state other than dictatorships, come and go. The people end up remembering. They will remember when our hospital ships were offshore caring for their injured, our air force was flying low overhead dropping supplies, and some of our forces wearing the flag on the ground were alongside them helping find/rescue or worst case put their loved ones to rest.
