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On Thursday, the Pentagon said it was tracking an alleged Chinese spy balloon flying across the US.

But the next day, China said the balloon was nothing more than a "civilian airship" which had deviated from its planned route, used for "mainly meteorological" purposes.

Montana, over which the balloon was flying, is home to some of the US's nuclear missile silos.

So how exactly did the saga over the spy balloon begin - and what are its implications? Jack Detsch, Foreign Policy's Pentagon and national security reporter, explains how it all started.

(Photo: An alleged spy balloon spotted over the US is a Chinese "civilian airship", China says. Credit: Reuters)