The Fourth of July reminds us not only to celebrate our democracy but also to assess the most serious challenges to it. These days, those challenges emanate less from home than abroad, and the United States should take appropriate action on the world stage to defend itself.

Rising autocracies in China and Russia as well as Islamist regimes in the Middle East and elsewhere are confronting the United States and its allies more aggressively. They have far different notions of freedom, democracy and human rights and, left to their own devices, they would create a world far less hospitable to our values.

The United Nations, meanwhile, is increasingly unwilling to promote those values, which we believe would create a safer world for America and a more prosperous one for people across the globe.

Consequently, the United States and other democracies lack an effective institution through which to pool their resources, identify their challenges, and define a strategy to protect their interests. It is well past time for America to lead the effort to create one.

Despite the outrage that it evokes in some U.N.-loving quarters, a so-called League of Democracies is hardly a new idea. Experts date it to the 18th-century Prussian philosopher Immanuel Kant and his notion of “perpetual peace.”

Nor, despite its strong endorsement by Republican presidential candidate John McCain, is the idea identified with just one political party. It was promoted by the Clinton and then Bush administrations, and it draws support from foreign policy experts of the right and left, be they members of Congress, former diplomats or scholars.

Clearly, the United Nations is not working for America and its allies. It is neither defusing the most urgent threats facing the West nor responding to humanitarian disasters that offend our sensibilities.

In the 192-member General Assembly, such blocs as the 115-member Non-Aligned Movement and the 56-member Organization of the Islamic Conference can gather the votes to thwart U.S. priorities. In the Security Council, any of five permanent members can veto U.S. proposals for collective action to confront threats to peace.

On the threat front, the Security Council continues to block the tough sanctions that might convince Iran to drop its nuclear ambitions. Permanent members Russia and China each have growing business ties with the Islamic republic as well as a shared geopolitical interest in keeping the United States mired in a struggle with the Islamic republic.

That means that the United States and its European allies, who face increasingly bold threats from Tehran, are subjecting their security to the whims of competing powers with competing interests.

On the humanitarian front, the Security Council could not agree on collective action to stop the killing in Rwanda, the Balkans, or Darfur, or the brutal suppression in Burma and Zimbabwe.

This will not do. The United States should jeopardize neither its security nor its values at the altar of a global body whose members resent America’s overwhelming power and influence.

The answer, however, is not for the United States just to act alone. Even our closest allies have little appetite for American unilateralism. And though uniquely powerful, the United States still can accomplish more in this world by working in partnership with our allies.

Thus, we need another global institution, one that truly represents the shared interests of the world’s democracies and, when the time for collective action has arrived, could legitimize it on the world stage.

To critics who worry that a League of Democracies would anger Russia, China and others who would feel disenfranchised, here’s the answer in one word: “Good.”

For what’s true of corporations is true of public institutions: competition can provide a useful jolt, convincing institutions to change and offering useful alternatives to those that refuse to do so.