Lantz (2013) identified that the Kruskal-Wallis test ... should be the primary [test] used to compare [differences]

Question:

Lantz (2013) identified that "the Kruskal-Wallis test ... should be the primary [test] used to compare [differences] when it is known that populations are not at least approximately normal". Explain why this statement is true for the Kruskal-Wallis test, and for nonparametric tests in general.