The cultural, political and historical relationships between Hungary and Slovakia are barely known outside the region. Disputed national identities and incompatible narratives of nation are at the core of the relationship. The Magyars of Hungary were once the dominant power in the region, ruling a disparate group of national minorities. Following the Ottoman occupation the Magyars came under German-speaking Habsburg rule, causing the Germanisation of Magyar culture, and culminating in the 1848-1849 Hungarian Revolution and War of Independence; this in turn resulted in the Ausgleich (kiegyezes or Compromise) of 1868, which gave the Magyars de facto autonomy over the lands of the Carpathian Basin. In 1918 the Habsburg monarchy collapsed and with it Greater Hungary. A much reduced Hungary emerged, alongside a Slovakia now a federal part of the new Czechoslovakia. This thesis argues that Hungary's most intimate Carpathian relationship has always been with Slovakia; for almost a millennium this was quite untroubled, but deteriorated drastically when Herder's romantic ideas penetrated the region, and further still when post-Ausgleich Hungary began the ethnic bullying of her minorities, particularly the Slovaks, in a process known as 'Magyarization'.