http://ryankett.hubpages.com/hub/The...s-In-The-World
USA VS China
Mainly depends on where the war takes place. If the USA were to attempt to invade China, we would lose, simply because they have more people than we have guns and bullets. (Exaggeration but the point remains). If it were any other type of battle, it would be a complete tossup. The US has superior technology on every front, but not as many resources. In a long drawn out war of attrition, China would win, hands down due to the amount of unprocessed and processed resources they have.
China VS Russia
Again, a tossup. The chances are completely likely that China would destroy Russia on every front, but one mustn't forget about the winter ;)
USA VS Russia
USA, if there is again, no invasion of the main country.
South Korea VS North Korea
Including or excluding external support? Including, it would stalemate again. Excluding, North and South Korea would no longer exist. It would simply be called "The People's Republic of Korea".
Spain VS Mexico
Mexico. Why? Mexican cartels. They're pretty damn nasty.
Japan VS South Korea
Completely impossible. Neither country has an army big enough to do anything to the other, added to the fact that both countries are protected by the same people, the USA.
Israel VS Egypt
Israel, but only if the surrounding countries don't get involved.
Britain VS India
India, if the war takes place somewhere that isn't the British Isles.
Switzerland VS Belgium
Switzerland. They may seem useless in a fight, but their defenses between the mountains and other factors is nigh impregnable.
Pakistan VS India
India, simply due to the fact that their economy and technology are far superior to that of Pakistan's. Although, surgical strikes (which would probably be considered acts of terrorism) could quite possible cripple the Indian war machine and lead Pakistan to a surprising victory.
Turkey VS Iran
Even though this would never happen, Iran due to their current technological advantages over Turkey.
EDIT:
Gonzo. The USA has around 400,000 more active duty soldiers than Russia.
Also, both Iraqs and Afghanistan were complete tactical successes. The failure lies in the withdrawal phase, as in, there was none. Planning was done to send the troops in, planning was done to have them do whatever they needed to do over there, however, absolutely 0 planning was done on how to get them out. They came, they saw, they asked 'what now', and got told "I don't know, maybe we should stay here". Either way, the tactical and operational processes were complete success stories. Then again, you're only talking about Vietnam, Operation Iraqi Freedom, and the War on Terrorism in Afghanistan. Did you mention Jordan, Libya, and Syria from the 80's? Nope. Did you mention Operation Desert Storm from the 90's? Nope. Why? Because they were completely successful and you just want to hone in on the failures; which to be quite honest is pretty nationalistic of you. Especially when you read further down that Britain would win over India due to 'troop training superiority', only further supporting my claim of your nationalism tendencies. What is nationalism? It's another 'ism', like racism, ethnic-ism, sexism, and should be thought of as such.

