Final answer:
In World War I, the subject of trenches and tank development in trench warfare is discussed.
Step-by-step explanation:
In World War I, the construction of defensive fortifications in trenches was a significant aspect of warfare. Both sides attempted to outflank each other's trenches to gain an advantage. The race to maneuver forces and construct defensive lines was referred to as the Race to the Sea. The use and challenges of tanks in trench warfare were also a notable development.