Why do we celebrate Labor Day?

In USA the day of labor day start from 1954 (may be the year in 1942 correct year before 1950 only) It is for restrict to working hour to labour for 9 hours including one hour rest. .It is started from U.S.A ONLY.

This is from wikipedia, it explains it better than I could. The first Labor Day in the United States was observed on September 5, 1882 in New York City, by the Central Labor Union of New York, the nation's first integrated major trade union.[1] It became a federal holiday in 1894, when, following the deaths of a number of workers at the hands of the U.S. military and U.S. Marshals during the Pullman Strike, President Grover Cleveland put reconciliation with the labor movement as a top political priority. Fearing further conflict, legislation making Labor Day a national holiday was rushed through Congress unanimously and signed into law a mere six days after the end of the strike.[2] The September date originally chosen by the CLU of NY and observed by many of the nation's trade unions for the past several years was selected rather than the more widespread International Workers' Day because Cleveland was concerned that observance of the latter would stir up negative emotions linked to the Haymarket Affair, for which it had been observed to commemorate.[3] All U.S. states, the District of Columbia, and the territories had made it a stautory holiday.