Why is 110V the standard for electricity in the US while in many other places it is 220V?

The reason we use 110 V 60 Hz is because of the Westinghouse Edison (War of the Currents) fight when both were trying to push their versions of electric power to the general public (AC vs DC). Edison went on a harsh campaign showing how dangerous AC electricity was versus his DC. AC was more dangerous because under DC power and low current, if you were shocked your body muscles reacted by flinching away from the shock. Whereas AC and high current caused the muscles to lock in position and cause the muscles of the victim to grab harder. Edison's problem for DC though was, because the voltage couldn't be stepped up with a transformer, that the wires and copper he needed to transmit DC over long distances would have required massive cables. This meant that the current in transmission was relatively large, and so heavy conductors were required and transmission distances were limited, to about a mile; otherwise transmission losses would make the system uneconomical. AC however could be stepped up in voltage and lowered current so that AC could be transmitted vast distances using thin copper lines with relatively little loss of power. Once the market determined that AC was to be the power source to power the US, the government started setting rules. After Edison's AC fear campaign, the government set the limit of household outlet voltage to 100 volts, +-10%, so Westinghouse set the limit for use to the max at 110V. Since Europe was starting to us electricity, but without the War of the Currents fear campaign, they chose a more economical system using 220 V that provided greater power and versatility for the household user.

edit* spelling and a P.S. Edison even electrocuted a prisoner facing the death penalty to show how dangerous AC was. Didn't work though, Prisons started using the Electric Chair to execute death row inmates because of his demonstration.