In the First, the brunt was taken by the French and by the British and Empire troops. In the Second the Americans were valiant lookers-on until December 1941. In both cases all the leading of the way had been done, with the US "willing to wound, and yet afraid to strike". To the old adage of "over-sexed, overpaid and over here" you could have added "overdue".
And you really cannot say that "liberty is man's natural and desired condition". Man's "natural" state is probably hierarchical, either familial or tribal. Humankind has always been constrained, originally by geography and harvest and the mutuality of effort involved in eking life out of them, now by conventions that echo those limits on where you can be and what sort of roof you can put over your head.
Liberty is an aspiration and you don't have to speak English to aspire, you only need to breathe.