Immigration has been one of the biggest issues in the on-going US elections, with Republican candidate Donald Trump building his entire campaign around the idea of keeping people out. Not counting his blatantly bigoted statements calling for all Muslims to be banned from the US, Trump has focused primarily on people making their way over America's southern border, from Mexico. The most recent figures, however, suggest that Mexico isn't even the biggest source of immigrants to the US. That position is held by India.

An analysis by the Wall Street Journal revealed that in 2014, the latest year for which US census data are available, more Indians immigrated to American than people from any other country. Mexico wasn't even in second place, with that distinction instead going to China.

These figures include both legal and illegal immigrants, and don't distinguish between the two. Specifically they cover the foreign-born population in America whose residence the year prior had been a country other than the United States.

In fact, the 2014 figures aren't even an outlier. Mexico didn't even come in at first place in 2013, when a historic shift saw both India and China eclipsing America's southern neighbour, thanks in part to a spike in Chinese immigrants. And the shift is indeed historic. According to the WSJ, as recently as 2005 Mexico was sending 10 times more people to the US as China and more than six times as many as India.

This graph, by Eric B Jensen of the US Census' population division, shows how big this change has been.

This doesn't mean there are more Indian immigrants in the US than Mexicans – not by a long shot. In 2014, there were 11 million people who had been born in Mexico in America, compared to just 2.2 million Indian-born people. What it suggests instead is that fewer Mexicans are now crossing the border to enter the United States, while Indians continue to migrate in droves.

Indian-born immigrants still make up only about 5.2% of America's immigrant population compared to Mexico's 27.9%.

These figures only look at those who were born outside the US and immigrated to the country. According to the Migration Policy Institute, the drop in Mexican immigration has been brought about by stronger border controls, a weaker US economy and better job opportunities in Mexico itself. Meanwhile, Indians continue to look to America as a land of opportunity while filling up the country's demand for high-skilled labour.

The institute reported in 2015:

"Indian and Chinese nationals are also the most common beneficiaries of the two main nonimmigrant work visas: the H-1B visa for specialty occupations (such as scientists, engineers, and computer programmers), and L-1 visas for intracompany managers, executives, and employees with specialized knowledge. Indian nationals were approved for nearly 70 percent of H-1B petitions and 30 percent of L-1 petitions in fiscal year (FY) 2014." 

As with the Mexican immigration concerns, this too has not been without its share of controversy. Recent changes in the US' H-1B policy, including doubling the fees and limiting the number of those who can apply, has been taken as aimed squarely at Indian workers whom politicians in the US are taking up American jobs.

Questions about America's visa policy regularly feature in talks between New Delhi and Washington and has been brought up by Indian-Americans too.