Other than diseases, what are other examples of contagious diffusion?

There are four types of diffusion. Relocation, Stimulus, contagious and hierarchical

The three steps before modern english were indo-european, germanic, and old english. as peoples moved around the eurasian continent, their languages changed. throughout the ages, the languages became more specialized. as english has many germanic influences, it is easy to see how this was one of the forebears. also, old english was one of the main ancestors of the modern language, spoken in the 5th through about the 13th centuries.