@book { DiehistorischeEntwicklungdesLandesNordrheinWestfalen,
    title = "Die historische Entwicklung des Landes Nordrhein-Westfalen",
    author = "Daniel {Schmale}",
    year = "2007",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783638617246",
    url = "https://www.hausarbeiten.de/document/70835"
}