Stjepan Radić, one of the most prominent Croatian politicians of the era, wrote in his 1917 book that of all Slavs, Bulgarians were closest to Croats.

However, Bulgarian–Croatian relations suffered in the pre-World War II Yugoslav state between 1918 and 1941, ruled by the Karađorđević dynasty, due to earlier conflicts between Bulgaria and Serbia.

But even after 1944, the friendly relations between the MPO – the organization of the Bulgarian Macedonian emigration, closely related to Ivan Mihailov's VMRO, and the Croatian clerical nationalist emigration continued, as they mutually fought against Tito's Yugoslavia for decades – including rejecting the Macedonian nation and language newly created by Yugoslavia after WWII.

[5][6] For the rest of the period prior to 1992, there had been no special crisis or event that required bilateral diplomacy from Croatians and Bulgarians as self-representing nations.

However, as two South Slavic nations in relatively close proximity, both nations have been party to some form of diplomatic mission throughout the centuries, whether between the Ottoman Empire and the Republic of Venice (which controlled Croatia's coastal region for some centuries), or during the 20th century when Croatia had been part of Yugoslavia and various attempts were made from within Yugoslavia and Bulgaria to incorporate Bulgaria into the Pan-South Slavic nation.