Plovdiv reached an agreement that the Principality of Bulgaria and Eastern Rumelia had a common government, Parliament, administration, and army. Today 6 September is celebrated as the Unification Day and the Day of Plovdiv. After the unification, Plovdiv remained the second most populous city in Bulgaria after the capital Sofia. The first railway in the city was built in 1874 connecting it with the Ottoman capital, and in 1888, it was linked with Sofia. In 1892 Plovdiv became host of the First Bulgarian Fair with international participation which was succeeded by the International Fair Plovdiv. After the liberation, the first brewery
Plovdiv was inaugurated in the city. In the beginning of the 20th century, Plovdiv grew as a significant industrial and commercial center with well-developed light and food industry. In 1927 the electrification of Plovdiv has started. German, French, and Belgian capital was invested in the city in development of modern trade, banking, and industry. In 1939 there were 16,000 craftsmen and 17,000 workers in manufacturing factories, mainly for food and tobacco processing. During the Second World War, the tobacco industry expanded as well as the export of fruit and vegetables. In 1943, 1,500 Jews were saved from deportation in concentration camps