Now that Canada has joined the war against the Islamic State in Iraq, some home truths beckon.

Canada has committed itself to six months of combat. Anyone who thinks the Islamic State can be pushed back in six months, let alone "defeated" (U.S. President Barack Obama's word), is seriously ill-informed.

Last week, the U.S. military and civilian leadership gave an off-the-record briefing in Baghdad. The New York Times reported the briefers saying it will be a "multiyear" campaign. In Syria, the briefers predicted that no ground campaign against the Islamic State could begin for 12 to 18 months.

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In the words of Anthony Cordesman of the Center for Strategic and International Studies, "the basic goal of degrading and defeating the Islamic State always bordered on the ridiculous." Air attacks, a more effective Iraqi army and even an improvement in the so-called "moderate" Syrian forces would still leave "some form of violent Islamic extremism." He says U.S. military officials have told him "that the struggle against violent religious extremism would go on for years, if not more than a decade."

In an excellent survey for the RAND Corp., Seth Jones has underlined how "Salafist-jihadi" groups have grown in size and number. Since al-Qaeda first gained international notoriety, these groups have split into four types: al-Qaeda itself, headquartered in Pakistan; groups affiliated with al-Qaeda whose leaders have sworn loyalty to it; other Salafist-jihadi groups; and inspired individuals (perhaps such as the Canadian terrorists who killed two soldiers last week) and networks.

Lumping these groups together is a fundamental mistake easily made by the media and politicians swimming in their own rhetoric. For example, Ayman al-Zawahiri, al-Qaeda's leader, cut off all ties between his organization and the Islamic State in February because it would not accept his leadership.

Groups affiliated with al-Qaeda exist in Yemen, Syria, Somalia and Algeria. These groups, and other sorts of terrorist organizations, differ greatly about how much, if at all, to target Western countries and interests. Some wish to concentrate on the "near enemy," states near to where they operate; others do want to strike Western interests that represent the "far enemy."

While obviously opposing Western countries, the Islamic State was more interested in the "near enemy" – that is, the governments of Syria and Iraq, replacement of which would allow the Islamic State to realize the dream of an Islamic caliphate.

By contrast, al-Qaeda targeted the United States through attacks on the American homeland and U.S. institutions abroad. It also hoped to lure the U.S. into overcommitment in Islamic areas, to "exhaust her and bleed her," in Mr. al-Zawahiri's words. With the U.S. involved in various ways in Afghanistan, Pakistan, Iraq, Syria and other Arab countries, the al-Qaeda strategy remains in place.

Those with dreams of a short war should reflect on Mr. Jones's finding that the number of Salafist-jihadi groups jumped 58 per cent from 2010 to 2013. They have particularly flourished in countries with weak central leadership, where previously strong leadership was shattered by internal dissent or Western intervention (Iraq, Libya).

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The U.S. State Department reports a 15-fold increase in terror attacks since 2002 and a threefold increase since 2010 in the Middle East and North Africa. The numbers do not include attacks in Pakistan and Afghanistan.

Six Canadian planes and those who fly and service them have been sent into the fight against the Islamic State, only in Iraq. Canadians might think this bombing campaign will do much good.

They should be made aware that, according to the U.S. briefing last week, targets other than stationary ones (oil refineries, bases and headquarters) are hard to find. The Islamic State has dispersed its forces and blended fighters with civilians.

The United States is flying fewer than 10 sorties a day in Syria and five in Iraq – compare that with the North Atlantic Treaty Organization air campaign in Libya, which carried out about 50 strikes a day. The limited number of targets, not any shortage of planes, is what accounts for the difference.

Air power alone is of marginal use without supporting troops on the ground. These are rare: a few Iraq units, Kurdish forces, a few Shia militias. And while the United States is bombing the Islamic State in Syria, President Bashar al-Assad's planes flew many sorties against his enemies, including the IS.

Mr. al-Assad, whom the U.S. wants out of office, is very pleased for the help.