You mean the crusades? It will be difficult to have such a thing happen in the twentieth century, unless the entire European continent goes Fascist/Genocidal on us.
It doesn't have to be necessarily European states (or America) deciding to launch a crusade, but at least a significant (10-20%) of their populations...or the populations of a sufficiently strong European state alone, thinking it is a good idea. I.E., have a bunch of American, British, Dutch, whatever, christians moving to the Promisland in order to establish a Cristian state there, perhaps in the interwar period...
Or maybe a Greek settlement after the collapse of the Ottomans.
Whatever way it could happen, have a significiant number of Chrstians think havng / establishing a Christian state in the Holy Land as important / religious duty...most pious of acts...