The largest and wealthiest cities in the Europe at the millennium were Muslim Cordoba and Byzantine Constantinople. The embryonic nation states of France and England were precarious, threatened by powerful neighbours. Repeatedly invaded by the Danes under the weak rule of Ethelred the Unready (r. 979–1016), England would then be absorbed into a Danish empire under Cnut (r. 1016–35). The France of the Capetians ensured its survival only by shrewd dynastic alliances. In Christian Spain, Castile waxed, Leon waned. Italy was an imperial cockpit, where Norman mercenaries would soon add an extra volatility to the mix. The decadent papacy was traded between thuggish aristocratic clans, the Tusculani and Crescenzii. The Holy Roman Empire had descended into instability after the death of Otto the Great (973), compounded by the emergence of a powerful Hungary (under St Stephen) and Poland (under Boleslaw the Brave) on its eastern borders. A resurgent Byzantium crushed the Bulgar Empire (1014).