Ankara is once more boldly appealing to the West to follow its lead in shaping policy in Turkey's volatile Muslim backyard. And again, Western powers are looking at Turkey with incredulity, waiting for Ankara to assume responsibility for the region by tackling the immediate threat of the Islamic State with whatever resources necessary, rather than pursuing a seemingly reckless strategy of toppling the Syrian government. Turkey's behavior can be perplexing and frustrating to Western leaders, but the country's combination of reticence in action and audacity in rhetoric can be traced back to many of the same issues that confronted Istanbul in 1919, beginning with the struggle over the territory of Mosul....