On April 20, 1854, Austria threatened to intervene in the Crimean War. Austria massed an army of 50,000 men in Galicia and Transylvania, after entering into a defensive alliance with Prussia against Russia. With Ottoman permission, Austria moved into the Danube principalities of Walachia and Moldavia. Threatened by this action, Russian forces abandoned the area in August 1854 but rejected the joint peace conditions set by England, France, Prussia and Austria (the Vienna Four Points issued on August 8, 1854) that Russia not interfere in the Ottoman Empire. Austrian forces continued to occupy Walachia and Moldavia after the end of the Crimean War, until March 1857.
During 1856, a campaign began for union of Walachia and Moldavia. The movement had the support of France, because many Romanian revolutionaries took refuge there after 1848 and lobbied Napoleon III to press for unification; Austria, Britain, and the Ottomans, however, opposed the unification effort, while Russia opted to let the Romanians decide. The Austrian withdrawal in March 1857 restored Ottoman suzerainty to the principalities.
In 1857 the Porte manipulated an election of delegates to special assemblies charged with discussing unification; the few voters casting ballots elected representatives opposing union. An international crisis followed, and Napoleon III, with Russian and British support, finally pressured the Ottomans to nullify the results and hold new, untainted elections, which returned a huge majority of delegates in favor of unification. These delegates immediately called for autonomy, a constitutional government, and a foreign prince to rule the unified principalities. Despite the election results, an international conference in Paris in 1858 reaffirmed separation of Walachia and Moldavia under Ottoman sovereignty, but it allowed for a common coinage and uniform laws and titled the two states the "United Principalities." The Romanians themselves overcame the imposed separation in 1859 when the separate assemblies at Bucharest and Iasi unanimously elected the same man, Alexandru Ioan Cuza, governor of both principalities. Distracted by war in Italy, the leading European nations yielded to a fait accompli and accepted unification, and Cuza (1859-66) became prince.