Which worked great! I think WW2 was the first great example of how wars have become unwinnable; Germany had success conquering large swathes of Europe through sheer force, overwhelming odds and not enough time to prepare, but they couldn't make it to the UK, and Russia was just too large, too long a distance, and too harsh a climate to have any chances.
More recent examples; Korea, Vietnam, Afghanistan, Iraq, Ukraine. None of which ended up in a decisive victory.