Final answer:
The slowdown in Allied advancement into France after the successful D-Day invasion was primarily due to overstretched supply lines, bad weather, and strong German defenses.
Step-by-step explanation:
While the D-Day invasion was a turning point in World War II, the Allied advancement into France slowed down in November 1944 primarily due to overstretched supply lines. The farther the Allied forces moved from the coast, the more challenging it became to transport supplies to the front lines.
Several factors contributed to this, such as bad weather and strong German defenses, but fundamentally, the infrastructure could not keep up with the rapid advance and the huge demands of the advancing armies. This logistical struggle was crucial in the subsequent tempo of the Allied push towards Germany.