Moreover, while the House of Grimaldi had close ties to France due not only to geographical proximity, but also to possession of estates (vaster by far than the territory of the principality) and financial investments there, nothing officially prevented the dynasty's political or cultural associations from focusing elsewhere. Moreover, the hereditary principle allocated monarchies according to one form or another of proximity of blood, and the Grimaldis' hitherto exclusive control of Monaco's dynastic marital policy was what threatened to enthrone a German duke on France's border, even after the Empire's defeat in war. Just as the ruling families of Britain, Russia, Belgium, and the Netherlands had all become patrilineally German by the twentieth century due to the propensity of monarchical heiresses, seeking dynastically equal marriages, to choose husbands from among Germany's many minor princely families, Monaco was on the verge of the same fate. Although the Grimaldis did not require inter-marriage with royalty by law as German dynasties typically did, by custom they never married subjects of their own realm, and no Monégasque reigning prince or heir had wed a French consort in more than a century.