How did the metric system come into place?

Answer 1

Earlier it was decided that 1 metre is the lenght of the cylinder of platinum-irridium alloy kept at Zero degree Celsius in The international beaureau of weights and measures at Serves near Paris

Later the definition was changed as to the distance travelled by light in 1/299792458 sec in air or in vaccum.

Answer 2

The metric system was first introduced in 1799 in France. The system is used in many countries across the world, but not in the United States of America.