There are several factors that support the argument that the war led to a decline in church attendance. The horrors and brutality of the war may have caused some individuals to question the existence of a benevolent and all-powerful God, leading them to abandon their religious beliefs. The war also led to a breakdown of traditional social structures, including the decline of the monarchy and the rise of secular ideologies such as communism and socialism, which may have contributed to a decline in church attendance.
On the other hand, there are also arguments to support the claim that the war actually led to an increase in church attendance. For many individuals, the war may have provided a sense of comfort and solace in the face of death and destruction. The war may have also led to a renewed appreciation for life and a desire for spiritual guidance, leading more individuals to seek solace in religion. Additionally, the war effort was often framed in religious terms, with both sides invoking God and religious imagery to justify their cause. This may have contributed to a sense of religious fervor and increased church attendance.
Ultimately, the impact of World War I on church attendance is a complex issue with no easy answers. It is likely that the war had both positive and negative effects on church attendance, and that the overall impact varied depending on individual circumstances and religious beliefs.