For the first time since the 1700’s Puerto Rico’s population has seen a historic drop as more islanders have left for the U.S. mainland than any time since the end of World War II. As of 2013, about a third of all people born in the island now live on the mainland, according to a Pew Research report.

“I would say it’s the first time we’ve seen a sustained population decline in the island even as far back as before Puerto Rico became a U.S. territory,” said Mark Hugo Lopez, director of Hispanic research at Pew Hispanic and one of the study’s authors, adding that the decline is projected to continue. Puerto Rico became a U.S. territory in 1898.

The Pew Hispanic Research Center study highlights the fact that Puerto Ricans have left the financially troubled island for the U.S. mainland this decade in their largest numbers since the Great Migration after World War II, citing job-related reasons above all others.

In 2006, Congress decided to end corporate tax breaks to American companies which invested in Puerto Rico, resulting in the loss of thousands of manufacturing jobs as companies cut back on employment. The resulting budget deficit led to steep government layoffs and sales taxes which impacted lower and middle income earners.

According to the Pew Study “U.S. Census Bureau data show that 144,000 more people left the island for the mainland than the other way around from mid-2010 to 2013, a larger gap between emigrants and migrants than during the entire decades of the 1970s, 1980s or 1990s. This escalated loss of migrants fueled the island’s first sustained population decline in its history as a U.S. territory, even as the stateside Puerto Rican population grew briskly.”

The search for economic opportunity is the most commonly given explanation for moving by island-born Puerto Ricans who relocated to the mainland from 2006 to 2013, according to a Pew Research Center analysis of U.S. Census Bureau data. A plurality (42%) gave job-related reasons for moving stateside, compared with 38% who gave family-related reasons. Among all immigrants from foreign countries who migrated over the same time period, a similar share gave job-related reasons (41%), while 29% said they migrated for family reasons. Mexican-born immigrants were even more likely to cite job-related reasons (62%), while 25% cited family reasons.

The Pew Center reports that “the departures of island-born Puerto Ricans have contributed to an uptick in the number of island-born Puerto Ricans living stateside, to 1.4 million in 2012, up from 1.3 million in 2000. The island born, however, are a smaller group than the faster-growing mainland-born Puerto Ricans, who numbered 3.4 million in 2012, up from 2 million in 2000.”

As the island population has dwindled and the mainland population has grown, the number of stateside Puerto Ricans reached a record 4.9 million in 2012, and since at least 2006 has exceeded the number of Puerto Ricans on the island (3.5 million in 2012). Meanwhile, the overall population in the U.S. territory of Puerto Rico, including both Hispanics and non-Hispanics, declined to 3.6 million in 2013, according to U.S. Census Bureau population estimates.