Short answers, pulled from the story.
The United States Federal Communications Commission convened the National Television System Committee in 1940 to resolve conflicts between competing companies. The committee issued its first technical standard for black-and-white television in March 1941.
The FCC replaced the incompatible CBS system on December 17 of that year with an NTSC color standard. Several companies including RCA and Philco helped develop this new compatible standard which aired publicly on the 30th of August 1953.
Engineers reduced the frame rate to accommodate a subcarrier frequency of 3.579545 MHz so horizontal line-rate modulation components fell between luminance signal components. This change amounted to just 0.1 percent but were tolerated by existing TV sets to ensure compatibility.
Most over-the-air NTSC transmissions in the United States ended on the 12th of June 2009 following an FCC requirement to shut down analog transmitters. The shutdown date moved later to June 12 of that year for full compliance after originally being set for the 17th of February 2009.
Paraguay Uruguay and Argentina chose PAL before adopting NTSC-N proposals. NTSC-N was originally proposed in the 1960s as a 50 Hz broadcast method for System N countries.