Final answer:
General John A. Lejeune experienced his first combat during World War I, deeply influenced by industrialization. World War I brought new levels of mechanized warfare and immense casualties, leaving indelible marks on soldiers and affecting the global power balance.
Step-by-step explanation:
General John A. Lejeune saw combat for the first time in World War I. This war was considered the first global conflict due to its wide-reaching impact on nearly all nations and was significantly influenced by the advancements of the Industrial Revolution. Despite its devastating nature, it was romanticized through images brought home to the civilians and contributed to significant geopolitical changes, including the transformation of national boundaries and shifts in global dominance.
During World War I, many American soldiers, including the men from the 369th Infantry Regiment, served under French leadership and took part in several key battles. Notably, these soldiers faced the industrial scale of death and destruction on a level that the world had not seen before, and the experiences and trauma they endured had long-lasting effects on the United States.
Military advancements of the time made warfare more mechanized and resulted in a high number of casualties, causing lasting physical and psychological damage to veterans and shifting the hegemony towards the United States and the Soviet Union after the war.