They share the world’s longest border, so it’s a darn good thing the United States and Canada have one of the best national security relationships in modern history.

Their partnership has produced more than 2,500 defense agreements addressing everything from data sharing to free trade. Unfortunately, agreement is conspicuously absent on one vital issue: protecting Canadians from a long-range ballistic missile attack.

For decades, Canada has refused to participate in U.S. long-range missile defense efforts. As a result, there is no legal framework that would allow the U.S. to shoot down a long-range nuclear-tipped missile headed for Canada. Ottawa has, however, endorsed missile defense protection for its European NATO allies. Somehow, what is good for the Europeans is not good enough for the Canadians.

It’s time to fix this.

Canada should invest in a long-range missile defense system and cooperate with the U.S. on expanding its existing missile defenses.

The threat is real.

Year after year, North Korea has steadily improving its long-range ballistic missiles. It’s only a matter of time until that weirdly unpredictable nation it will bring all Canadian and U.S. territory within reach of its missiles. Worse, the U.S. Defense Intelligence Agency believes that North Korea already possesses nuclear weapons suitable for delivery by ballistic missile.

Canada endorsed missile defense for her European NATO allies for a different, though still pressing, reason: the Iranian ballistic missile threat had become intolerably real.

With technical assistance from Pyongyang, the mullahs in Tehran have busily advanced both their ballistic missile and nuclear weapons programs. Keeping allies vulnerable would simply be playing into the hand of a regime that calls America “the Great Satan” and has repeatedly called for the destruction of Israel.

Canada has rebuffed repeated American overtures seeking cooperation on missile defense, most recently in 2005. The view in Ottawa seems to be: “If the world’s rogue regimes opt to attack the West, surely they’ll aim at the U.S., not us — and they already have a defense system in place.”

If only rogue nations were so predictable — and accurate. Think of missile defense as home (or rather homeland) insurance. Just because your neighbor owns a hose doesn’t mean that you shouldn’t buy one yourself — especially if you’re neighbor hose doesn’t reach as far as your house.

The likelihood of a ballistic missile being launched has escalated dramatically since the end of the Cold War, due to the spread of ballistic missile and nuclear technologies. Two years ago, Gen. Charles Jacoby, chief of NORAD, reported that “tangible evidence of North Korean and Iranian ambitions reinforces our understanding of how the ballistic missile threat to the homeland has matured from a theoretical to a practical consideration.”

Ottawa’s refusal to participate has put Canada in a bizarre position. Currently, Canadian military authorities can help detect an incoming missile, but they have no input into a decision about what to do after it’s been spotted, even if that missile is headed directly for Ottawa.

The Canadian and U.S. economies, electrical grid, and security are inextricably linked. A successful ballistic missile attack on either would cause incredible damage to both. Should a nuclear weapon detonate at high altitude, the resultant electromagnetic pulse could devastate our electrical grid and communications links. It would change life as we know it, dramatically and not for the better, on both sides of the border.

The Canadian government does not have to reinvent the wheel. The U.S. has already undertaken a long and expensive R&D program. Missile defense technology has been proven — to the point that about 30 long-range missile interceptors are deployed and protecting the U.S. homeland today. These interceptors could be used to protect Canadian cities, provided that the Canadian government is interested in cooperating.

Contra the naysayers, U.S. missile defense deployments have triggered neither international arms races nor the weaponization of space. Rather, what has been observed over the years is how Israel’s short-range missile and rocket defenses have been a stabilizing influence in the world’s most persistently unstable region.

Missile defense enhances security and reduces the risk of war. It is time to extend these benefits to Canadian citizens.

Originally appeared in the National Post.