14th century, some time after the founding of Wallachia. By then, the institution of slavery was already established in Moldavia and it was possibly established in both principalities. After the Roma migrated into the area, slavery became a widespread practice among the majority of the population. The Tatar slaves, smaller in numbers, were eventually merged into the Roma population. Some branches of the Romani people reached Western Europe in the 15th century, fleeing from the Ottoman conquest of the Balkans as refugees. Although the Romani were refugees from the conflicts in southeastern Europe, they were often suspected of being associated with the Ottoman invasion by certain populations in the West because their physical appearance was exotic. (The Imperial Diet at Landau and Freiburg in 1496–1498 declared that the Romani were spies for the Turks). In Western Europe, such suspicions and discrimination against people who constituted a visible minority resulted in persecution, often violent, with attempts to commit ethnic cleansing until the modern era. In times of social tension, the Romani suffered as scapegoats; for instance, they were accused of bringing the plague during times of epidemics. On 30 July 1749, Spain conducted The Great Roundup of Romani (Gitanos) in its territory. The Spanish Crown ordered a nationwide raid that led to the break-up of families because all able-bodied men were interned in forced labor camps in an attempt to commit ethnic cleansing. The measure was eventually reversed and the Romanis were freed as protests began to erupt in different communities, sedentary Romanis were highly esteemed and protected in rural Spain. Later in the 19th century, Romani immigration was forbidden on a racial basis in areas outside Europe, mostly in the English-speaking world. In 1880, Argentina prohibited immigration by Roma, as did the United States in 1885. Forced assimilation In the Habsburg monarchy under Maria Theresa (1740–1780), a series of decrees tried to integrate the Romanies in order to get them to permanently settle, removed their rights to horse and wagon ownership (1754) in order to reduce citizen-mobility, renamed them "New Citizens" and obliged Romani boys into military service just as any other citizens were if they had no trade (1761, and Revision 1770), required them to register with the local authorities (1767), and another decree prohibited marriages between Romanies (1773) in order to integrate them into the local population. Her successor Josef II prohibited the wearing of traditional Romani clothing