Nationalistic drive is a great way to convert "that politician took away 2% of power from this politician" into "that nation offended our nation!!!1one1!" without any new facts happening. It's especially important within a democracy, because war would need huge popular support - and that support needs to be manufactured by media by pushing any emotional buttons available.
"Why, of course, the people don't want war. Why would some poor slob on a farm want to risk his life in a war when the best that he can get out of it is to come back to his farm in one piece. Naturally, the common people don't want war; neither in Russia, nor in England, nor in American, nor for that matter in Germany. That is understood. But, after all, it is the leaders of the country who determine the policy and it is always a simple matter to drag the people along, whether it is a democracy, or a fascist dictatorship, or a parliament, or a communist dictatorship.
Voice or no voice, the people can always be brought to the bidding of the leaders. That is easy. All you have to do is tell them they are being attacked, and denounce the pacifists for lack of patriotism and exposing the country to danger. It works the same in any country."
Historically that is false. The common farmer might want to come back to the land - but his younger brother needs to leave the farm because it can't support him! Thus those younger brothers have nothing to gain by coming back to the farm. Their gains can only be found in being really great at something the city needs (cities are less than 5% of the population because farms don't have enough surplus to support more than that, so this is worse than farming), or winning a war and making a farm on the enemies land. If the war is fought to a stalemate, but only one of the two brothers returns back to the farm that is okay too.
The sexist language is historically correct. Sorry ladies, history wasn't kind to you in general.
For a war to be supported by people (soldiers, and in democracies, civilians as well), they need to view the other side as the Other side. The Enemy. The Others.
Nationalism is about building a strong us/them split, about having people internalize clear categories of Our Nation and The Others. This directly facilitates war.