Timmy811 said:
Not enough given the logistics involved. The Union had four times the white population of the South as well as four times the industry and could supply their forces over land and look how long that war lasted.
The US was trying to occupy the south (and the South crippled itself trying, if the US had offered the South a peace where they, the CSA, lost bits they had claims on, like Kentucky, the war would have been over far sooner because it isn't worth crippling your economy just to hang on to some lightly settled regions) Britain is going to be trying to conquer the US, just seize bits around the edges they want and then force the US to the table.
Anyway I see your civil war and raise you a war of 1812 where pitiful British forces (in quantity) were able to handle the US with ease.
Britain has to supply it's troops over a 3,000 sea line because Canada won't be able to supply the forces needed by itself and
Guess what you need to supply an army in a foreign country, Ports at home and abroad (Portsmouth, Plymouth, Falmouth, Bristol, Liverpool, Belfast, etc etc etc and Quebec, Halifax on the other side) and ships (now I think Britain might have some of those about but I could be round, does anybody recall whether Britain had any trading vessels about that they might be able to hire???).
it most keep substansial forces posted in Indian and other posts around the world.
How substantial?
And given that the UK starting available forces are bigger than the US and that the UK has a bigger population (and economy and industry) I would back them to be able to field the bigger army.