What did winston churchill mean by this?
"but if we fail, then the whole world, including the united states, including all that we have known and cared for, will sink into the abyss of a new dark age"

It means that if the Armed Forces and the British people (at great sacrifice) of Great Britain fail, then the whole world will change for the worse and a new age full of unknown horrors will be thrown into a deep dark inescapable  pit. Even the United States, with all its, power, will not escape this fate.

The Dark Ages were a particularly black period in Western Civilization's history. Education was frowned upon and those working in agriculture (most people) growing the food we need, were no better than slaves to the Church and to the Nobility.

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