Why did millions of people leave Italy and Austria-Hungary at the beginning of the 20th century?

By the beginning of the 20th century, these states were secondary to the economy of Europe. Not all of their regions were industrial, many remained agrarian, which meant a high birth rate and unemployment, so the population that could not find themselves in Italy and Austria-Hungary left, for example, to the USA, Argentina, Uruguay. In these states, either the level of socio-economic development was higher or there was more free land.