Donald Trump said Monday that if elected he would "suspend immigration from areas of the world when there is a proven history of terrorism against the United States, Europe or our allies, until we understand how to end these threats."

What would this latest version -- there have been several -- of the GOP presumptive presidential nominee's proposed ban look like? And how many people would it affect? The short answer is millions. Here's the math, including nonimmigrant and immigrant visas from countries that have any sort of terrorist activity:

Start with 'terrorist safe havens': 12 countries; 496,436 nonimmigrant and 74,283 immigrant visas in 2015

The State Department's annual report on global terrorist activity lists 12 "terrorist safe havens" around the world where "terrorists are able to organize, plan, raise funds, communicate, recruit, train, transit and operate." These safe havens include Somalia, Mali, Libya, Egypt, Iraq, Lebanon, the Philippines, Indonesia, Malaysia, Afghanistan, Pakistan and Yemen.

Total countries so far: 12

Add 'state sponsors of terror': 3 countries; 45,935 nonimmigrant and 10,722 immigrant visas in 2015

An additional three countries -- Iran, Sudan and Syria -- are designated as state sponsors of terrorism.

Total countries so far: 15

Nations where terror networks are based and operate: 14 countries; 1,741,169 nonimmigrant and 63,106 immigrant visas in 2015

The report lists a further 14 countries where terrorists operate or are based, though are not considered "safe havens." This list becomes broader since terror groups ranging from ISIS to al Qaeda and its affiliates have successfully recruited and infiltrated numerous operatives and cells into countries ranging from Turkey and Russia to Nigeria and India.

Total countries so far: 29

Other countries with active terror cells: 11 countries; 295,695 nonimmigrant and 16,883 immigrant visas in 2015

The State Department's list does not include countries that have smaller though substantial presence of jihadis or suspected jihadis, such as France, Belgium or the U.K., each of which has dozens of known terror cells and hundreds of known and suspected terror suspects. A total of 11 countries fall into this category.

Final tally: 40 countries

The State Department granted 2,571,762 nonimmigrant visas to residents of those 40 countries in fiscal year 2015. State also granted 158,877 immigrant visas to individuals from those countries in that same period.

Citizens from some of these countries, such as France, Belgium and the U.K., do not require visas for tourist travel to the U.S. More than 7.5 million tourists from these countries traveled to the U.S. in 2014, according to data provided by the Department of Commerce.

All told, as many as 10.2 million people could be barred from the U.S.