From 1861 thru 1865, the US Military was being fed by the military draft & was on a massive war footing...fighting the civil war. This time frame was probably the only time in the 19th century (1800s) that the US was a very powerful nation.
Any nation engaged at war, is at that moment in time, at their strongest and most alert. The US most probably had the best military in the 1860s, possibly even in the world.
Britain had been fighting across the globe from India to Afghanistan (Khyber Pass), from China (Opium Wars) to America (War of 1812)...but all of those actions paled to the US Civil War (in size and scope).
France or Great Britain
Since Britain was an established military and national empire; it simply had to destroy what they considered a "new" military, and a "new" un-civilized nation. They intended to defeat the US on the battlefield, and then destroy it's national capital. Both were done...but the war was nearly a draw anyway.
The US provided war material of all kinds to the Allies,
It could be China , Russia , America or Britain China has the most men. The US has the best technology, equipment, and vehicles. Britain is a little ways behind them, and Russia is a little ways behind them. So overall the US has the best military. Really depends on who's answering the question. Editor - NoOne can say , not even soldiers or anyone with military experiance , no one knows the hole world... or anything about the military , so do one buddy.
The US would have lost the only English speaking European Nation as an ally. Which would have hindered future communication with the European Continent. There would have been no major military consequences, as Britain LOST it's military prowess at the end of WW2.
lend-lease. Britain leased the US bases in the Caribbean and the US provided Britain with much needed supplies.
the Us was better than the vietcong in military it was guerilla warfare that was over the Us
treaty of Alliance
In the 21st century, the US military is the most powerful in the world.
Britan because god was British
Save Great Britain FIRST; Britain will support ALL US Military basing & supplies; save Europe next.
the Chinese because they have men
US has better navy for it has 12 aircraft carriers unlike Britain who only has ships that can launch harriers.
Military service for women
Treaty of Alliance
This is probably classified information so it is unlikely that you will get a complete answer.
Treaty of Alliance