Time: January 19, 1922
Place: Guatemala City
A year earlier the Pact of Union between Costa Rica, Guatemala, Honduras, and Salvador had been signed at San Jose. This declared a perpetual and indissoluble union between the countries. V. Martinez of Guatemala was the first President but not even that persuaded the Guatemalans to accept the union. On December 8, 1921 revolution erupted. It’s success brought down the government and the union dissolved.
Central America was united in other periods since independence. This revolution ended the federal movement in this part of the world.
More information: Wikipedia