Personally I want to know how we 'have to fight' 1.5 billion anyone to begin with. AFAIK, we are on the opposite side of the planet as 1.5 billion Muslims. The only ones we HAVE to fight are the ones already here when they go Jihadi.
Now the only way that number increases if, say, some bleeding heart liberal works to import more of them. Since they have no navy capable of transporting multiple Normandy level invasions, they have to rely on cruise ships and commercial airlines.
And those require passport/Visas.
Seems to me, as usual, the biggest threat to America comes from within. Leftist enablers. Simple math really.
It isn't the 1.5 billion we have to worry about, it is more like the 80 million in Iran, and the 190 million in Pakistan that will be the most serious threat.
Iran is just on the cusp of getting Nuke ICBMs. A significant segment of the Iranian Leadership belong to a particular sub cult of Islam. They are like the Westboro Baptist Church version of Islam.
They believe that it is their duty to assist in the return of the Mahdi. They believe that the Mahdi is destined to return in the Islamic version of the final conflict between good and evil, and they believe that the Mahdi will lead a heavenly host and sweep away all the infidels with fire, and that a total Islamic peace will descend upon the Earth, to be enjoyed by the now totally Islamic world, forever and ever.
They also believe that if they trigger this massive cataclysmic by fire, *that* will bring the return of the Mahdi. In other words, start a world wide nuclear war, and Allah will bless and reward them.
The Soviets were power hungry oligarchs, but they didn't want to die. These people are bat-sh*t crazy religious fanatics, and they absolutely want to die if they can burn the great Satan with fire.