Argentine general Juan Lavalle makes a coup against governor Manuel Dorrego, beginning the Decembrist revolution.

Juan Galo Lavalle was an Argentine military and political figure from the Unitarian Party.

Manuel Dorrego was an Argentine statesman and soldier. He was governor of Buenos Aires in 1820, and then again from 1827 to 1828.

The Decembrist revolution was a military coup in the Buenos Aires Province, Argentina. Juan Lavalle, returning with the troops that fought in the Argentine-Brazilian War, mounted a coup on December 1, 1828, capturing and killing the governor Manuel Dorrego and ultimately closing the legislature. The rancher Juan Manuel de Rosas organized militias that fought against Lavalle and removed him from power, restoring the legislature. However, as the coup had reignited the Argentine Civil Wars, Rosas was appointed governor of the Buenos Aires province to wage the war against the Unitarian League. Both José María Paz, from Córdoba, and Rosas formed a league of provinces. The conflict ended soon after the unexpected capture of Paz, when he mistook enemy troops for his own.