>>628003
>World War 1
Same outcome, shittier economic situation afterwards.
>World War 2
Uncertain. Probably would have found some other workaround with even worse long term consequences if I recall the UK only finished paying back its WW2 loans in ~2008.
In both cases it was in the USA's interests to corner the trade routes nobody else could afford to protect or pay attention to while remaining neutral then join the war and contribute enough to help dictate the outcome and terms.
Now a much better question is what would have happened without the USA's material support, WW2 in particular would have ended very differently since the USSR was nearly entirely reliant on allied aid for logistics the UK also benefited heavily but was itself sending some to the Soviets and as an island was never under quite as deep a threat outside of starvation. I'd suspect a halted German advance then a stalemate where the USSR could not make ground until either the Germans ran out of stockpiled resources ironically the USSR was their only serious source of supplies or some form of decisive political shift e.g. UK backing out of the war on very favourable terms changed the playing field.