World War I was one of the most horrible wars in history. Because of this, it had a terrible impact on many of the soldiers. Of course, millions of soldiers were simply killed or wounded. The war impacted them in obvious ways. But even many of those who came through unscathed physically were traumatized by the things that they had seen. This can be seen in the poetry of such people as Sigfried Sassoon (who survived the war) and Wilfred Owen (who did not).
In America, at least, some of the soldiers were impacted in a different way. They were exposed to a whole new way of life that they had never seen before. In this way, the war broadened their horizons. This can be seen in title of the song that asked "How Ya Gonna Keep Them Down on the Farm? (After They've Seen Paree)." In this way, the war had a less negative effect, at least on some soldiers in the US.