According to its description, Category:Germany, Emigrants should not have person profiles, so I started categorizing profiles in this category into lower level categories. In the case of Johan Wilhelm Crolius, this resulted in "Category:Migrants from Principality of Wied to Province of New Jersey", which was immediately deleted again. Could someone with better skills than mine please create that category including appropriate parent categories so that Johan Wilhelm receives his correct migration category? Thanks!
Okay, I went to „Space:Migration Category Structure“ to read up on the guidelines, then found Grafschaft Wied on Wikidata and created Category:County of Wied, Emigrants accordingly. Mission accomplished! ;-)