I was thinking about how we (USA) are always in continuous (ghost) wars and never try to negotiate for peace, to my knowledge.

The US has supported or started many pointless wars, but that we have never negotiated for peace or avoided war is not accurate. One example is that the US, as part of the UN, participates in peacekeeping efforts across the world.

One country and one languague or would a world power have to forcibly join everyone together?

So, you know that 'one world government' is a thing that terrifies a lot of religious conservatives because they think it means the antichrist and the end of the world, right? The language thing is difficult too. From what i recall the most common language worldwide is Spanish, with 2.5-3 billion people speaking it, which means 5 billion or so people would have to learn Spanish, or we'd have to pick some other language and even more people would have to learn that. (EDIT: oops, English is #1 followed by Mandarin. I somehow confused Spanish with Catholicism)

I agree that nationalism is harmful, but overall it would be very, very difficult to persuade every country in the world to give up their language and national identity. Also, as central planning doesn't work very well, any world government would have to be segmented to provide effective governance for regions, which would mean basically... like now... each region has it's own government.

Most likely the reasonable thing to do would be to try to encourage countries to work together peacefully, rather than try to abolish nations.