Thanks for adding, folks.

The best explanation I have ever seen for the date is:

With 2 million Russian soldiers dead in the war, Russian women again chose the last Sunday in February to strike for "bread and peace". Political leaders opposed the timing of the strike, but the women went on anyway. The rest is history: Four days later the Czar was forced to abdicate and the provisional Government granted women the right to vote. That historic Sunday fell on 23 February on the Julian calendar then in use in Russia, but on 8 March on the Gregorian calendar in use elsewhere.

Since those early years, International Women's Day has assumed a new global dimension for women in developed and developing countries alike.