Iran’s growing influence in the region has been cause for concern for both Arabs and Israelis alike, and the Trump administration is laying out a plan to create a so-called “Arab NATO,” in part to counter that expansion, according to US and Arab officials. The idea to pull together a multinational Arab force is nothing new. Efforts to foster regional military cooperation date back to the Arab League’s founding in 1945. Since then, regional military efforts – like the 1991 Gulf War and the 2011 intervention in Libya – have largely come under outside leadership and seen modest Arab military participation. Even in the current US-led coalition against ISIS, some Arab regimes are dragging their feet. Disparate interests, conflicts among them, lack of a credible threat to their territories, and a dearth of leadership have prevented the realization of a true operational alliance.In 2015, the Arab League agreed to form a combined military force to counter both Iranian influence and Islamist extremism. Later that year, Saudi Arabia announced the formation of the 34-nation Islamic military alliance for the fight against terrorist organizations, such as Islamic State. Despite these ambitious plans, nothing has yet materialized.Saudi Arabia succeeded in forming a military coalition with other Gulf states to combat the Iranian-backed Houthis in Yemen, but the war has dragged on without conclusive results and with charges that the coalition is responsible for significant civilian casualties and humanitarian deprivation. The kingdom has been unable to recruit the biggest Arab army – Egypt’s – or the biggest Muslim military force – Pakistan’s – to commit to the task.The most obvious cause of alignment is a desire to combine members’ capabilities in a way that furthers their ability to tackle a perceived common threat. But besides shared interests, the group needs dominant military and political leadership – that of the United States. Indeed, Washington has found it in its interest to support attempts to balance Iran by the use of local forces, but it needs to be realistic in its goals.For the US, a regional coalition could prevent, or limit, putting American boots on the ground and would be much cheaper, both financially and diplomatically, than direct US deployments. A regional military force could, in theory, broaden its missions to also include fights against Iran’s subversion, support for terrorism and weapons-smuggling. But sometimes a common enemy is simply not enough. Unity among the Arab states has been difficult to come by.LONGSTANDING TRIBAL, family and interpersonal rivalries, territorial disputes and different positions with respect to Iran and the Muslim Brotherhood, have caused discord between Saudi Arabia and Egypt; between Oman and other Gulf Cooperation Council (GCC) states; and between Qatar and, well, everyone.At times, America’s allies in the region – Arabs and Israelis united by a common enemy – express the worry that the US, in a bipartisan trend that has crossed administrations, is trying to distance itself from its leadership role in the Middle East. In fairness, both the Obama and Trump administrations maintained and continue to maintain a robust presence of US forces in the Gulf region, adding new capabilities, such as missile defense systems as needed. The US has also provided extensive sales of advanced US weapons technologies to its regional partners. But even that sustained commitment should be accompanied by constant assurance.The Trump administration should remain practical and realistic about the capabilities of its regional partners, and encourage US allies to coordinate, train and plan so that when needed, they can perform uniform security actions. CENTCOM planners are uniquely positioned to assist in these efforts. To further curb Iran’s influence, a common intelligence and operational military framework should be undertaken. When they take place under American leadership, such actions are another way to enhance America’s credibility, as well as its image of strength and deterrence ability.But it is unrealistic to expect the countries involved to commit themselves to coming to each other’s aid in a manner resembling NATO’s Article 5. Neither the capabilities nor the political unity is yet in place to make such commitments reliable or meaningful.Witness the Egyptian military’s difficulties rooting out ISIS cells in Sinai, and imagine them coming to the aid of a neighbor under duress. Or consider the divisions that have riven the GCC over the past year, with several members aggressively boycotting Qatar. Now take into account that these are only the most recent chapters of a long history of disunity.The bottom line is that the United States’ interests in broader regional stability – and its ability to check the aggression and violence of hostile actors from Iran and terrorist organizations – can be significantly advanced by upgraded coordination, joint training, intelligence sharing and interoperability of its regional Arab partners. But expecting that to blossom fully into an NATO-style alliance of Arab states, thereby absolving the United States of its regional responsibilities, will remain a fantasy.Daniel B. Shapiro is a distinguished visiting fellow at the Institute for National Security Studies. He served as US ambassador to Israel and senior director for the Middle East and North Africa at the National Security Council during the Obama administration.Dr. Yoel Guzansky is a senior fellow at the Institute for National Security Studies. He previously served in the Prime Minister’s Office.