The United Nations has once again lost its power to act. Russian President Vladimir Putin has brought back Cold War-era paralysis to the Security Council.

Putin’s determination to oppose the U.S. and its allies at the U.N. on almost every issue, large or small, means that virtually no meaningful resolution can pass. When a resolution does pass – as with the Security Council-mandated ceasefire in Syria – Putin simply ignores it if he chooses.

The West must come to terms with this new reality and accept that it will now have to act directly in its own interests – without the cover or support of the U.N.

For a while, things were different. The U.N. played an important role in several conflicts over the past three decades. Its resolutions authorized action in 1991 to liberate Kuwait from Iraqi dictator Saddam Hussein's invasion. The U.N. then imposed a strong weapons inspections regime on Iraq, backed by the authorization to use military force, throughout the 1990s.

In addition, the U.N. imposed increasingly harsh sanctions against Iran for its nuclear program, helping drive Tehran to accept the nuclear deal offered by the Obama administration in 2014. President Obama's wisdom or folly in signing that deal does not reduce the fact that U.N. sanctions hurt Iran badly enough to help force it to the table.

Those days are gone. The U.N.'s relative effectiveness depended on the willingness of Russia to support or at least accede to Western actions against former Russian clients (such as Iraq in 1990-1992) and potential allies (like Iran in 2006-10, when the sanctions regime expanded dramatically).

Putin has now taken a position of outright opposition to the West, however, and will no longer accept such actions. He will not permit the Security Council to punish his ally, Syrian dictator Bashar Assad, for despicable war crimes against his own people. In fact, Russian air forces may well have collaborated in some of those war crimes.

Putin also will not allow the U.N. to pressure Iran to stop the expansion of its own military and proxy forces throughout the Middle East. And he will prevent the world body from taking meaningful action in Yemen, Iraq, Syria and Lebanon that Iran deems harmful.

An example of this is Russia’s recent veto of an effort to condemn obvious Iranian violations of sanctions preventing weapons transfers to Yemen's Houthi rebel movement. This effectively removes the U.N. from a theater in which concerted international action is urgently needed. Millions are suffering as a result.

The U.N. has one tooth left with regard to Iran that Putin cannot easily remove – snap-back sanctions linked to the Iranian nuclear program. The Security Council resolution implementing the nuclear deal provides that sanctions automatically return if a signatory to the deal asserts that another party has violated it unless the Security Council passes a new resolution extending the sanctions relief.

Since the U.S. (as well as France and Britain) could veto any such resolution, Putin cannot prevent the reimposition of the full force of pre-deal international sanctions on Iran. This is a strong card the U.S. can threaten to play in addressing the nuclear deal’s many defects.

Russian aggression toward its own neighbors offers the clearest proof that the days of U.N. authority are gone. Putin invaded Georgia in 2008, has occupied and even annexed portions of it to the Russian Federation – and the U.N. took no meaningful action.

Putin invaded and annexed Crimea from Ukraine – and the U.N. took no meaningful action. Russia invaded and still supports militarily proxy forces in eastern Ukraine – and the U.N. took no meaningful action.

And Putin could invade the rest of Ukraine tomorrow, or the Baltics or any other state – and the U.N. would likely take no action because Putin would veto any effort to do otherwise.

The sooner Western leaders and elites come to terms with this reality, the better. The U.N. can no longer provide the legitimacy for action against aggression that many look for. It cannot effectively mediate disputes between permanent members of the Security Council. Its resolutions cannot be the litmus test for the legality of actions in defense of international norms or even law in most cases.

Those who oppose aggression and oppression must turn to their own interests and consciences to determine their actions. They must form their own coalitions and rely on their own strength. We can and should aspire to end the enmity that has created this situation, but we can have little hope of succeeding any time soon.

The weakening of the U.N. increases the need for strong alliances. NATO and the bilateral alliances America has with Japan, South Korea, Australia, and its other Asian partners become more vital than ever as the world order frays.

Collective action for the foreseeable future will mean alliance action, not U.N. action. The White House and leaders on both sides of the U.S. political aisle must make every effort now to strengthen and expand alliances rather than allowing economic, social or other disagreements to weaken them.

The worst possible situation for America is a world in which the U.N. is paralyzed and our allies alienated. The world does not need another impotent League of Nations and an isolated America.