GMT became the standard just because they did it first. Sort of. Lots of countries used a local meridian as their 0 degrees reference for longitude. Then in 18

GMT became the standard just because they did it first. Sort of. Lots of countries used a local meridian as their 0 degrees reference for longitude. Then in 1884 there as the International Meridian Conference (https://en.wikipedia.org/wiki/International_Meridian_Conference https://en.wikipedia.org/wiki/International_Meridian_Confere...) which chose Greenwich as the reference line. The same conference also voted to have midnight be the start of the day for astronomical and nautical purposes (instead of noon). The French objected to using Greenwich and hung on to the Paris meridian until into the 20th century. But the practicality of lots of maps using Greenwich (because of Britain's naval power) swayed people to have Greenwich as the Prime Meridian.