We started out as a 110V country, thanks to Tom Edison. He picked a nice round number, 100V for DC distribution, and then added 10%, 110V total. The first AC systems maintained the 110V DC standard (in VAC RMS, of course), and over time the nominal distribution voltage has crept upward as (a) it permits more efficient use of the distribution network and (b) it allows the power company to sell more electricity.
If one wishes to be more pedantic, Edison's original DC system was actually +/- 110V, with a neutral/ground. But from what I recall reading, only 110V was made available to customers, some got +110V and others -110V and none had 220V DC.
If you look at old equipment nameplates or catalogs, you will see the nominal line voltage stated as 110V (really old), 115V, 117.5V and now 120V. My line voltage used to run 123-124V but after the power company reworked its local distribution network a couple years ago, it's almost always within 1V of 120V.
My UPS power supply has trip points at 135V / 95V, and within that range it will not switch to inverter.