Vlado Chernozemski- the guy who caused World War 2?

 Had Archduke Ferdinand been killed by a Muslim- Muhamed Mehmedbašić- rather than an Orthodox Christian Serb- there would have been no First World War because the Turks would have got the blame. Sadly, Mehmedbasic's nerve failed. He didn't chuck the grenade he had in his hand as the Archduke's car passed by. 

Similarly, if Vlado Chernozemski- a Bulgarian who killed the King of Yugoslavia in 1934- had not accidentally also shot the French Foreign Minister- Louis Barthou- maybe there would have been no Second World War.

This is because Barthou was negotiating the Franco-Soviet mutual assistance pact. After his death, the task of completing it fell to Pierre Laval- later executed for his collaboration with the Nazis- who had moved to the Right & who considered the Bolsheviks as a great threat to European Civilization.

De Gaulle would write '"Louis Barthou had thought of a return to the traditional system of Russian alliance. But he was assassinated, and from that moment on, the policy of abandonment prevailed. Our leaders, caught between the fear of war and the illusions of peace, surrendered themselves to the stream of events..."

Barthou had got the Soviet Union into the League of Nations and wanted a comprehensive multi-lateral 'Eastern Pact' to pen in Germany and preserve the existing borders. The Brits were suspicious of Barthou's plan but he was able to win over Stanley Baldwin causing him to say that Britain's frontier now lay along the Rhine. 

The Brits saw Laval as an opportunist but considered him to be pragmatic and transactional. Sadly, the Hoare-Laval pact (which sacrificed Ethiopia to Mussolini) provoked a backlash at home. Baldwin threw over Hoare & Laval, quite naturally, felt betrayed. 

Laval didn't believe that the Soviet Union had the military capability of Tzarist Russia. Though the Soviets were embracing mechanisation, he didn't believe there could be a 'Russian steam-roller'. Thus he ensured that the bilateral treaty agreement was strictly compatible with the multilateral provisions of the League of Nations Covenant and the Locarno Treaties. That in practice meant that military assistance could be rendered by one signatory to the other only after both an allegation of unprovoked aggression had been submitted to the League of Nations, and the approval of the other signatories of the Locarno Pact (the United Kingdom, Italy and Belgium) being attained. Even this was only agreed to by Laval after Germany announced its re-armament. Poland, however, reacted strongly. They refused to accept any scenario where Soviet troops crossed Polish territory. They considered the pact to be a betrayal of the 1921 Franco-Polish agreement. They sought to rely on their non-aggression pact with the Soviets (1932) and with Hitler (1934). Partly, this was because France had earlier refused to act jointly with Poland in a pre-emptive strike. De Gaulle, who had been an official observer during the Soviet-Polish war, had great respect for Pilsudski and favoured a more robust approach. But, as the Poles could understand, France needed Britain which now repented the harst peace terms imposed on Germany and which was in no mood for military adventures. Once Barthou established good relations with Baldwin- based on convincing him of the Nazi threat- it is possible that Poland would have revised its views. Sadly, the Brits were obsessed with the notion that Mussolini could be a counterweight to Hitler based on an exaggerated notion of Italian military strength. It may also be the case that Pilsudski's death meant Poland took a harder line not just against the Soviets but also the Czechoslovaks (Poland had lost some territory in the 7 day Czech/Polish war of 1919). Later, they would help themselves to a piece of that unfortunate country along side Hitler & Horthy .

Some historians- notably Robert J. Young- who wrote a biography of Barthou- & Jean-Baptiste Duroselle- considered a leading expert on the diplomatic history of the period- treats Barthou as the sole "hero" of French interwar foreign policy (vide his seminal work, France and the Nazi Threat: The Collapse of French Diplomacy 1932–1939.) 

Another foundational giant of French international history, Pierre Renouvin, meticulously mapped out how Barthou was systematically pooling all the European powers threatened by the rapid revival of Germany. Renouvin’s analysis supports the idea that Barthou's strategy was highly cohesive—simultaneously locking in the USSR, securing British support, using Italy’s fears of an Austro-German union (Anschluss), and solidifying the Little Entente (Czechoslovakia, Romania & Yugoslavia) . Renouvin concludes that Barthou's sudden assassination shattered this entire interlocking system. 

Michael Jabara Carley, an expert on Soviet foreign policy and Franco-Soviet relations,  emphasizes that Barthou's approach was the only window in the early-to-mid 1930s where a genuine anti-Nazi containment front could have succeeded. Carley’s research highlights that Maxim Litvinov (the Soviet Foreign Minister) found a reliable, hardheaded partner in Barthou. He notes that after Barthou's death, his successor Pierre Laval allowed anti-communist domestic pressures to stall and dilute the alliance, transforming a potentially robust military guarantee into a toothless piece of paper. 

It is a silly to think some random French dude could have prevented a World War. The truth is, it was the Spanish Civil War which provided the template for what would come. There, the French PM- Leon Blum- initially tried to help the Republicans but internal opposition- as well as British disapproval- forced him to renege. In France there were those who said 'better Hitler than Blum'. Suddenly, every Nation State had to fear an ideological 'fifth column'. 

Still, if Barthou could have been Europe's saviour (just as the Archduke is sometimes seen as the guy who could have saved the Hapsburg Empire by giving the Southern Slavs a better deal), then it is significant that a Serb & a Bulgarian put an end to European hegemony thus laying the foundations for the rise and rise of the 'coloured' races.