During Donald Trump's CNN interview with Anderson Cooper the other day, Cooper asked whether Trump thought the West is at war with Islam itself or just radical Islam.  Trump replied: "It's radical, but it's very hard to define. It's very hard to separate because you don't know who's who."

I'm not an expert on world religions, but I do have several books in my library on that subject.  One of them is A History of the Jews by Paul Johnson, published in 1987.  Page 175 is instructive:

When [the Jews] refused to acknowledge [Mohammed's] prophetic mission, he applied the principle of what he called the jihad. This divides the world into the dar al-Islam, the peaceful territory of Islam, where the law [sharia] reigns, and the dar al-Harb, the "territory of war," controlled temporarily by non-Moslems. The jihad is the necessary and permanent state of war against the dar al-Harb, which can only end when the entire world submits to Islam.

Even though the context here is Islam's treatment of Jews over the centuries, Johnson's points have general application.

1. According to Mohammed, Moslems have an absolute moral and religious obligation to bring about worldwide domination by Islam, by any means necessary.  The failure to act on this obligation is taken very seriously.

2. There is no distinction in Islam between "radical" and "non-radical."  There is nothing to define.  One should not buy into the notion that we need a scorecard to separate "the good Moslems" from "the bad Moslems."  There are only Moslems.

3. The 75% of Moslems worldwide who are not actively engaged in jihad, the so-called "peaceful Moslems," are in fact guilty of a mortal sin under Islam.  Attacks against them by ISIS or al-Qaeda are intended as a reminder of this fact and as a wake-up call.

4. The 75% are not taking action to restrain the 25% who are actively engaged in jihad not just because they are afraid of retaliation.  Many Moslems agree with the jihadists and provide assistance through mosques and other means.

5. Moslems living in what Islam calls dar al-Harb countries such as the United States, though they obey our laws, nevertheless place allegiance to Islam above allegiance to our flag and would act accordingly if the opportunity arose – one day, maybe as a group.

6. The Fort Hood and San Bernardino terrorists were acting on their obligation to further Islam's domination as required by Mohammed.  So were the terrorists who brought down the World Trade Center and crashed into the Pentagon on 9/11.

7. There was no need to qualify Trump's point that the United States should halt Moslem immigration "until we know what's going on."  We already know what's going on.  Changing immigration laws is the answer – the sooner, the better.

I don't know if Paul Johnson would agree with all of the above points though it's pretty clear they are consistent with (or follow from) what he wrote.  By the way, Johnson received the Presidential Medal of Freedom from George W. Bush in December 2006.