Which war has the most countries involved?

Depends on how you do the stats historically people might think Britain or one of the other European powers but isn't the case because all of these wars were against rebels and less inferior opponents or Britain allied itself with others to win wars. Famously Britain has had a tough time against the Russians and France as they lost a lot of these wars. If you look at who alone beat the best around then you have to look at romans, mughals who more or less beat everyone that was tough around them more so mughals because Romans never won/conquered the chinese, japanese and had tough times against the Russians whereas the mughals ruled some parts or all of these countries barring Western Europe they didn't get that far but also Europe was in the control of Romans at that point.