Buenos Aires also attracted migrants from Argentina's provinces and neighboring countries. Shanty towns (''villas miseria'') started growing around the city's industrial areas during the 1930s, leading to pervasive social problems and social contrasts with the largely upwardly-mobile Buenos Aires population. These laborers became the political base of Peronism, which emerged in Buenos Aires during the pivotal demonstration of 17 October 1945, at the Plaza de Mayo. Industrial workers of the Greater Buenos Aires industrial belt have been Peronism's main support base ever since, and Plaza de Mayo became the site for demonstrations and many of the country's political events; on 16 June 1955, however, a splinter faction of the Navy bombed the Plaza de Mayo area, killing 364 civilians (see ''Bombing of Plaza de Mayo''). This was the only time the city was attacked from the air, and the event was followed by a military uprising which deposed President Perón, three months later (see ''Revolución Libertadora'').