Can wakanda defeat USA?

Wakanda would wreck us. They have sonic spears that obliterate tanks. Personal energy shields. Rhinos covered in Vibranium.

Who would win in DC vs Marvel?

DC Comics would certainly win in a direct clash. Sure, Marvel might have the One-Above-All, but DC’s Doctor Manhattan is the most powerful and invincible fictional character ever created, and that is simply why DC Comics would win in this clash, despite the individual differences that might give points to Marvel.

Could the Avengers have defeated the Chitauri without the nuke?

Remember two things, first, America is what defeated the Chitauri invasion, not the Avengers. S.H.I.E.L.D. is an American agency, and without the nuke that S.H.I.E.L.D. launched, the Avengers would have been overwhelmed and destroyed.

What kind of weapons do the Wakanda troops use?

The Nazis had more advanced weapons in those secret Hydra labs then were in Wakanda, powered by tessaract energy, yet they were overwhelmed and destroyed repeatedly using conventional weapons and, in the end, conventional forces storming in. Same situation here. The Wakanda troops use what essentially are the staff weapons from Stargate.

Why did the Black Panthers want to hide Wakanda from the US?

You have to remember that in the movie, former Black Panthers sought to hide Wakanda because they were afraid of invasion. The main antagonist wanted to invade the rest of the world and showed through his actions and intent exactly why he was thrown out of the US specops community.

What would have happened to the Avengers without the nuke?

S.H.I.E.L.D. is an American agency, and without the nuke that S.H.I.E.L.D. launched, the Avengers would have been overwhelmed and destroyed. The US has the resolve needed to win in this situation, having had the resolve to nuke downtown New York City. Second, Captain America: The First Avenger.