According to a graph on wikimedia, and the corresponding wikipedia page merging of municipalities applied to an extreme scale in western germany between 1972 and 1979. Most states had less than 1/3 municipalities they had at the start of the decade. Even the two states who resisted this trend, Schleswig-Holstein & Rheineland/Pflatz, still had a rapid decrease, but only by 20%.
Why did this happen so sudently ?