Serbo-Croatian was standardized in the 19th century based on the Štokavian dialect. Since the breakup of Yugoslavia in 1991, the four national variants are standardized separately.
The differences between Serbian, Croatian and Bosnian are minimal. They are all mutually intelligible, though they have slightly different syntax, vocabulary and pronunciation. Additionally, Croatian is generally written in the Latin alphabet, while the others also use the Cyrillic alphabet.