On October 3, 1929, the Kingdom of Serbs, Croats and Slovenes was officially renamed Yugoslavia, and the country was divided into nine banovinas whose boundaries followed rivers and watersheds rather than the old provincial lines. King Alexander had suspended the constitution on January 6 of that year, dissolved the assembly and banned parties organised on a national basis. The new name was the point of the exercise.
The state had been assembled in December 1918 out of Serbia, Montenegro and the South Slav lands of the Habsburg empire, and it had never worked as one political unit. The Vidovdan constitution of 1921 made it a centralised state with power in Belgrade, and the Croatian Peasant Party under Stjepan Radic refused to accept it. Radic was shot in the assembly in June 1928 by a Montenegrin deputy. He died two months later. That is when the parliamentary system stopped functioning.
Alexander's answer was a royal dictatorship, justified at the time as the only way to hold the country together after a decade of obstruction and political murder. He abolished the historic provinces, banned the national flags and party names, introduced a single Yugoslav nationality in law, and set up a special court for the protection of the state. Several thousand people went through it in the first two years.
Integration from above backfired. The Croatian Peasant Party went underground, and the Ustase, the Croatian fascist movement that would run the Independent State of Croatia from 1941, was founded in 1929 in response. The Internal Macedonian Revolutionary Organisation, which had been fighting since the 1890s, kept fighting. Alexander was assassinated in Marseille in October 1934 by a VMRO gunman working with the Ustase.
The banovina boundaries were redrawn in 1939 under the Sporazum, the agreement that gave Croatia a large measure of autonomy inside the kingdom. It came too late. Yugoslavia was invaded in April 1941 and carved up, and the country that re-emerged in 1945 under Tito was a federation of six republics, which is the structure that broke apart in the wars of the 1990s.