Throughout U.S. history, from the Monroe Doctrine straight on to the end of the Cold War, there's been one overarching pillar of American foreign policy. The United States claimed the western hemisphere as its exclusive sphere of influence, and all other powers should stay out. U.S. strength applied to everything: land, sea, and air.

It doesn't matter if you're an isolationist or a military hawk that seeks expansive U.S. engagements. The base for each position in American foreign policy is the United States having total control of the western hemisphere. If you're an isolationist, you claim that America is strong at home and has no reason to meddle in foreign affairs that pull it away. If you're an expansionist hawk, you argue that America is safe domestically, which allows us to spread our powers outward.

With the United States shooting a fourth Chinese object out of the sky either over U.S. airspace or headed here, the integrity of this foremost pillar of American policy is challenged. American airspace and control of the western hemisphere are challenged for the first time since September 11, 2001, or the Cuban Missile Crisis. Prior to those events, you'd have to go back to the world wars to find similar incursions.

Monroe Doctrine established American superiority.

President James Monroe announced the Monroe Doctrine in his seventh year. He was the last Founding Father to serve as President. Echoing George Washington's farewell address, Monroe said, "In the wars of the European powers in matters relating to themselves we have never taken any part, nor does it comport with our policy to do so. It is only when our rights are invaded or seriously menaced that we resent injuries or make preparation for our defense. With the movements in this hemisphere we are of necessity more immediately connected."

Monroe then declared that the United States would focus on its own borders and countries in its hemisphere, leaving the Europeans alone: "to the defense of our own, which has been achieved by the loss of so much blood and treasure, and matured by the wisdom of their most enlightened citizens, and under which we have enjoyed unexampled felicity, this whole nation is devoted."

Americans so thoroughly liked and embraced this mindset that every President since has broadly agreed to follow it. We've seen expansions of it at times. For instance, Teddy Roosevelt called for his "corollary" to the Monroe Doctrine, which sought to combat European incursions into South America. Ronald Reagan expanded it again with the conflict against the Soviets, aiming to support countries and groups that opposed the Soviets while opposing those that helped it.

But these were responses to the unique challenges of the time. Once those challenges are gone, many Americans seek to fall back on the Monroe Doctrines, with few exceptions (Ukraine and Russia are current exceptions).

Monroe Doctrine demands a response.

The Monroe Doctrine is not just an isolationist stance, however. It calls for a strong response when America gets directly threatened. As mentioned, the Japanese attack on Pearl Harbor, the Cuban Missile Crisis, and September 11, 2001, were all direct violations of American sovereignty.

These Chinese spy balloons are incursions into American air space, directly challenging American sovereignty and security. Incidentally, the southern border falls into this space too, which is why many Americans want more security there. We are not an attempt to be a borderless European Union in the western hemisphere.

The Chinese Communist Party is directly challenging and flouting American airspace. They aren't just floating balloons over America. They're challenging U.S. superiority in these skies while saber rattling over Taiwan.

In a report, the Wall Street Journal says the fourth balloon shot down "was shaped like an octagon and that it was at an altitude of 20,000 feet, posing a threat to commercial aircraft. It did not appear to have a payload." Compared to the first balloon, which was in the 60,000 feet range of altitude, China's response is bringing their spy tech closer.

Chinese challenge American domestic airspace.

At first blush, instead of stepping back, the Chinese are escalating their use and placement of the balloons. NBC News suggests that NORAD is simply bad at its job, reporting, "After the Chinese surveillance balloon was downed this month, the U.S. military is now looking at a wider range of radar data as it monitors North American airspace, and is looking at more objects and smaller objects that it might have filtered out as clutter in the past, two U.S. Defense officials told NBC News."

If that last report is correct, NORAD is seriously letting down the American people and her leaders. The military's blunders don't excuse inaction on the first balloon. But it does show there are serious security holes in our domestic defense.

In either case, we're seeing much more invasions of U.S. airspace. Those actions challenge U.S. hegemony in the western hemisphere and must get met with force. For U.S. foreign policy of all stripes to preserve its legging, domestic security must be maintained.

The Chinese aren't just floating spy balloons over American airspace. They are challenging a central tenet of American policy. I hope our leaders answer this challenge head-on.