With all due respect most people making posts on this subject do not have a clue, the UK and US would win a conventional war at a canter.
Firstly in order to fight a war you need money, the US dollar is the world reserve currency meaning most international transactions are denominated in USD, meaning all the US needs to do when it wants to purchase essential war material from the international markets is to print some more dollars, the US also spends more than the next seven largest powers combined on defence. A simple glance at the numbers on here shows the disparity in budgets http://www.globalfirepower.com/defense-spending-budget.asp
The US, UK and Russia are amongst a small handful of countries with global expeditionary warfare capability, meaning the ability to project a large combined arms military battle group to any point on the planet and to sustain that battle group logistically, China does not yet have this capability, the Chinese can of course operate in Asia.
One of the key elements to winning a war is control of sea supply routes, the key to dominating the sea are attack submarines and air superiority, the US has the most submarines in the world and all are nuclear powered meaning they can operate for far longer than diesel powered subs.
The UK also has an all nuclear powered submarine force; while Russian and China have nuke and diesel powered fleets, see http://www.globalfirepower.com/navy-submarines.asp.
The US has 19 aircraft carriers, 10 being super carriers that carry 75 aircraft each; even the so called helicopter carriers have jets (harriers)
Air superiority is the key to winning any modern war, in-fact no state on state full scale conventional war has been won without control of the skies, Vietnam does not count as the US would have invaded North Vietnam if it was a full scale war, however that could have started WW3 hence why they didnโt, had they invaded the north then the war would have been won.
The disparity in numbers is even more clear in the air http://www.globalfirepower.com/aircraft-total.asp The US has 13,444 aircraft in its air force compared to Russiaโs 3,547 and Chinas 2942, that is more than Russia and China combined without counting the UKโs 879. The US also has more fighters, attack helicopters, transport helicopters etc.
So Russia does not even hold a numbers advantage as some of you seem to think.
Everybody also seems to agree that the US and UK has a technological advantage in terms of aircraft.
The only area that China and Russia enjoys a significant number advantage is in main battle tanks, however without control of the skies, it would be a turkey shoot as per Gulf war 1, when Iraqi tanks were shot to pieces on the highway out of Kuwait.



