There is ample reason for concern.  What began as a limited military assistance program to Kyiv from the United States and its European allies following Moscow's expanded invasion of Ukraine in February 2022 has morphed into something much larger and more dangerous.  NATO members are no longer just supplying Ukraine with weaponry that could arguably be described as purely defensive; they are equipping their Ukrainian proxy with far more destructive, long-range weapons capable of reaching targets deep inside Russia.  In addition, the United States and other NATO governments are assisting Ukrainian attacks by providing crucial military intelligence, including targeting data.

By engaging in that conduct, the United States is violating some informal but very real rules governing previous proxy wars that Washington has waged against adversaries.  One especially significant taboo barred attacks against the homelands of either the United States or its great power rival.  By allowing Ukraine, much less members of NATO, to be involved in attacks inside Russia, Washington has trashed that prohibition. Such reckless behavior threatens to entangle America and NATO as a whole in the Ukraine war as an outright belligerent against a nuclear-armed Russia and risk triggering World War III.

The conflict in Ukraine is hardly the first proxy war in history or even during just the period since the end of World War II.  Such ploys go back to the days of the Roman Empire and probably earlier.  The Korean War in the early 1950s had distinct features of a proxy war. Josef Stalin's regime in the Soviet Union pushed its North Korean client to attack the Western-backed government in Seoul in an effort to unite Korea under communist rule.  Washington (along with a few close allies) intervened to thwart that offensive and prop-up its anti-communist protectorate in South Korea.

The conflict threatened to become much more than a Korean civil war or a proxy war between the United States and the Soviet Union, however.  Matters escalated sharply when Moscow's prominent ally, communist China, intervened with its own troops.  That development highlighted how clients, especially significant powers with their own policy agendas, can create a perilous situation during a proxy war even if the homelands of the two main players remain off limits.  At one point, U.S. leaders considered attacking China, perhaps even using nuclear weapons.  Such a move might have transformed the existing proxy war on the Korean Peninsula into a direct armed conflict between the United States and the Soviet Union.