It's probably a couple of weeks too late to be discussing Labor Day. But having lived abroad for much of the last decade, and having experienced first hand the riotous street celebrations on "May Day" each year in London, I've repeatedly wondered why we in America celebrate Labor Day in September every year, while much of the rest of the world celebrates 'International Workers' Day' on May 1st. Now I've learned why, finally.
Labor Day has been a Federal holiday in the United States since 1894. It origins go back to the Haymarket Riot in Chicago on May 4, 1886, when a public demonstration in support of striking workers turned violent. In 1889 an international socialist organization meeting in Paris called for annual protest marches to be staged all over the world commemorating this Haymarket Riot, to begin the following year.
After a severe financial crisis in America in 1893, on May 1, 1894, riots broke out among the unemployed of Cleveland, Ohio, and then, just a few days later, on May 11, 1894, the famous Pullman Strike by railway workers was called. US President Grover Cleveland quickly reconciled with this increasingly activist (and disruptive) labor movement, and six days after the end of the Pullman Strike Congress rushed through legislation declaring Labor Day to be a Federal holiday. The September date was chosen specifically to avoid the day turning into an annual commemoration of these famous workers' strikes and riots, and to avoid direct association with international socialism.
As a result, we in America now have a quiet day of BBQs in September each year, marking the effective end to summer, while anarchists and students riot in London every year on May 1st.