In April, president of Zimbabwe, Robert Mugabe, praised China for its investment in his country: “I am pleased to report that significant headway has been made with a number of investment projects that have been funded by China now at various stages of implementation in all the key sectors of our economy,” he said in remarks delivered to the annual Zimbabwe International Trade Fair.

At first, this might seem like an insignificant development in world affairs — an incident in a part of the world that most Americans know little about and that policy-makers think has little impact on our national interests. But it is indicative of a broader and disturbing trend in global politics.

Those who argue that America has lost its moral authority and thus has squandered its claim to international pre-eminence, would do well to look towards Africa to see what the world might look like if America were to retreat from its global commitments.

Over the past several years, China has increased its trade, foreign aid, and military assistance to a host of disreputable leaders in Africa. There are no better examples of what Chinese foreign policy means than looking at how China has interacted with Zimbabwe and the Darfur region of Sudan.

With Western sanctions on his country, Mr. Mugabe has turned to China as his bastion of support. The Chinese are Zimbabwe’s second largest trading partner, behind South Africa, with $275 million worth of transactions last year in telecommunications, tobacco, and other agriculture. Chinese businessmen are so numerous in Zimbabwe that the southern part of the country’s capital, Harare, is referred to as “China City.”

Zimbabwe’s ties to Africa go far back to the days when Mr. Mugabe was a guerrilla leader fighting for independence against the white minority regime in then-Rhodesia and his primary backer was the Chinese communists. And China’s significance to Mr. Mugabe has only increased as his abuses have worsened.

When the international community marginalizes Mr. Mugabe and his regime, the Chinese step in to fill the void. According to the Chinese government, China was not even among Zimbabwe’s top 10 trading partners just a few years ago. Yet, as Zimbabwe’s humanitarian and political situation has deteriorated, the Chinese have increased their involvement.

The Chinese have provided riot gear and training to Mr. Mugabe’s police forces. They offer Tiananmen-style expertise in dealing with pro-democracy activists as well as huge shipments of fertilizer to maintain whatever can be salvaged of Mr. Mugabe’s reckless land seizure policies.

Last month, at a ceremony held at Mr. Mugabe’s presidential compound for a visiting Chinese delegation, the Zimbabwean dictator announced that his country’s enemies “would want to attack us, but we stand together with China.” In return, Mr. Mugabe pledged to pressure his African neighbors to cease support for Taiwan.

But the malevolence of China’s support for Mr. Mugabe pales to its aiding and abetting the genocide in Darfur. The Chinese are Sudan’s largest trading partner, and have stuck with the murderous regime in Khartoum.

China, ravenous for fossil fuels to develop its burgeoning economy, gobbles most of Sudan’s oil output. Last month in Beijing, the Chinese Defense Minister told Sudan’s army chief of staff that their military relations had “developed smoothly” and that they “are willing to further develop military co-operation between our two countries in all areas.” Meanwhile, the United Nations and the Western world have called for sanctions and an arms embargo against the Sudanese government.

Those who believe that America should minimize its global presence because our war against Iraq or our detention policies have made us unpopular must separate these qualms from the real-world considerations of global politics. If America were to retreat from the world stage, there is no question as to which power would step up in our place: China.

The rosy picture of a world in which all nations share equal burdens and responsibilities may be a comforting vision, but it is a fictional one. Unhindered by the notions of basic human and private property rights, the strength of civil society, or any of the other concerns with which the American people lobby our government, the Chinese are the epitome of the unscrupulous international actor.

The idea of America remaining as the only superpower may not be in favor right now, but those who think that need to answer the question: who would replace us? The alternative is dreadfully worse.

Mr. Kirchick, who reported from southern Africa last year, is assistant to the editor-in-chief of the New Republic.