A century ago Sunday, Germany declared war on France, setting in motion the bloody series of events that would leave millions dead across Europe and would set the stage for an even larger, costlier global conflict — World War II — a few decades later.

100 years later, a radically different world commemorated the beginning of World War I online.

Some Twitter accounts, including @RealTimeWW1, are retroactively live-tweeting the events of the conflict.

Some have changed history, in a manner of speaking, by colorizing the old black-and-white photographs that chronicle the war’s beginning and progress.

For others, the centenary offered a chance to remember ancestors who fought in the brutal struggle.

More than 65 million men were mobilized across the world during World War I, as the Central Powers of Germany, Austria-Hungary, Turkey and Bulgaria fought a much-larger coalition that included Russia, the British Empire, France and the United States.

Of those many millions mobilized, it is estimated that more than half were killed or wounded.

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