Suddenly Ecuadoreans, Brazilians, Nicaraguans, Venezuelans, Haitians and Cubans are turning up by the hundreds of thousands, a trend that accelerated sharply in the past six months.

From October 2020 through August, nearly 300,000 migrants from countries other than Mexico and the Northern Triangle were encountered at the border, a fifth of all crossings. For all of fiscal 2020, when the pandemic slowed the flow of migrants, the figure was nearly 44,000, or 11% of crossings. In fiscal 2019, it was 77,000, or 9% of crossings; and the year before it was only 21,000, or 5%. As recently as 2007 such migrants represented less than 1%.

Among the fastest-growing groups are Haitians. From October of last year through this August, about 28,000 Haitians were arrested trying to cross the U.S.-Mexico border. That is six times the 4,400 arrested during the entire 2020 fiscal year that ended last September.

The broad wave includes single mothers from Ecuador, Nicaraguan teenagers and farm laborers in Chile. Many cite the same reasons for uprooting their lives and heading north: economic hits from the pandemic that cost jobs and income, the allure of a booming U.S. economy and the belief that President Biden’s administration would welcome them.