Western nations can either learn this the easy way, or they can learn it the hard way.
Here in the United States, it appears we've chosen the hard way. Our fearless legislators in Congress, in their zeal for "immigration reform," have proposed every reform but the one that will keep America safest.
Close the door. No more immigration.
That will stop the flow of people coming to America, who, deep in their hearts, detest America. Had Tamerlan and Dzhokhar Tsarnaev been anywhere but America on April 15, the Boston Marathon bombings never would have happened.
Two more Western countries that seem determined to learn the hard way are the United Kingdom and Sweden.
By now, most, if not all readers have seen the video of two Muslims hacking a British soldier to death on the streets of London. British police have arrested two suspects: 28-year-old Michael Adebolajo and Michael Adebowale.
Both are accused of murdering British soldier Lee Rigby, whose widow said in a news story that she thought her husband would be safe on the streets of London.
The Lee Rigbys of the world — and the dead and wounded in Boston — will never be safe as long as Western nations insist on letting droves of people into their countries that hate their countries.
It was Adebolajo who was seen on a video giving his anti-Western, anti-British rant. Waving a meat cleaver that he allegedly used to hack Rigby to pieces, Adebolajo gave the world this message:
"I swear by almighty Allah we will never stop fighting you. We must fight them as they fight us."
A very brave British citizen named Ingrid Loyau-Kennett tried to reason with the suspects to prevent them, she said, from attacking anyone else.
Here's what she said one of them told her when she asked why they had killed Rigby:
"He said he had killed the man because [Rigby] was a British soldier who killed Muslim women and children in Iraq and Afghanistan. He was furious about the British army being over there."
Sound familiar? The Tsarnaev brothers carried out their act of terrorism supposedly for the same reason that those transplanted British suspects hacked Rigby to death.
But, for all their passion about Muslims in Afghanistan and Iraq and about Western nations being in Islamic countries, have you noticed neither the Tsarnaev brothers nor the British suspects chose to live in a Muslim country?
If Islam's the big deal they claim it is, then they should have ensconced themselves comfortably in a Muslim country. Instead, they chose to settle in predominantly Christian, Western democracies.
They chose to settle in countries they detest. Why? Because those countries allow them to, of course.
They'll come to the United States, a country they hate, and rant and rave about our foreign policies. And some of them will plant bombs.
They'll go to the United Kingdom and hack soldiers to death. They'll go to a country like Sweden and then riot.
Yes, Sweden is learning the hard way, too. Within the last two weeks, riots have wracked the suburbs of Stockholm. The rioters, according to the BBC, are immigrants that come from places like Turkey, the Middle East and Somalia.
"Rioting on this scale is unprecedented for the Swedish capital and has raised questions about the success of the country's attempts to integrate foreign-born residents, who now make up 15 percent of the population," the BBC said.
Integration? How about "deportation"?
Had Tamerlan Tsarnaev been deported when the FBI first got wind that he might be up to no good, would the Boston bombings have happened?
Both Adebolajo and Adebowale were on the radar of the British intelligence unit known as MI5. Had they been deported, Lee Rigby would still be alive.
Too bad the Brits had to learn that the hard way.
Washington Examiner Columnist Gregory Kane is a Pulitzer-nominated news and opinion journalist who has covered people and politics from Baltimore to the Sudan.