Flat, arid and clear-skied Iraq is accessible by sea and ideal for air operations. Landlocked Afghanistan is mountainous and hard to supply, with a harsh climate and often stormy weather. A nuclear and duplicitous Pakistan plays far more havoc than did even Iraq's meddling neighbors. Iraq has a stronger secular tradition, and its population is mostly literate. Afghanistan is far more fundamentalist and tribal, with well over half the population illiterate.
There were other differences in the two surges as well. The Iraq surge was overseen by hawkish and stubborn George W. Bush, who was not about to see the war that he started lost. Bush believed that a constitutional Iraq was key to spreading change elsewhere in the autocratic Arab world.
Although antiwar candidate Barack Obama campaigned against the Iraq war and promised to focus on Afghanistan, he clearly believed that most Americans wanted out of both wars as quickly as possible. As soon as Obama announced his own Afghan surge, he also promised to set dates for withdrawal. Fairly or not, both our military and the enemy concluded that American departure, rather than securing the country, was the overriding concern.
Four American generals have commanded operations in Afghanistan in a span of less than three years -- a far different scenario than Petraeus' continued tenure during the surge in Iraq. Americans are also tiring of the war: When Petraeus took over in Iraq, we had been at war almost four years; 2011 saw the 10th anniversary of an exhausting war in Afghanistan.
Finally, we still do not know all the reasons why Iraq quieted in 2008 and 2009. But there may have been ancillary factors for the surge's success. A steady increase in Iraqi oil revenues helped. In 2006, well before the surge, many fed-up Sunni leaders had abruptly joined Americans and turned on the murderous Islamic terrorists in their midst. And by 2007, Americans had cumulatively killed thousands of Islamists and ex-Baathists.
In other words, simply adding more troops and changing tactics might not have been the entire story of success in Iraq. A surge alone in Afghanistan likewise may not so easily turn things around without other such positive developments.
Continuity of American command, an ironclad commitment from the president to finish the job, diplomatic and military unity, and far more help from everyday Afghans are critical to the surge. Without all that, more troops and better tactics still will not bring the sort of success that we saw in Iraq.