The arrogant country called Great Britain managed to wreck the development of many countries but nothing worse than wrecking the development of European countries out of an attempt to retain a so-called power balance. Thanks to the frail Britons' concern of retaining power balance, they helped the Turks stay in Europe and Anatolia, plague European countries such as Bulgaria (with a Turkish minority of 12% or 700,000) and Germany (with a Turkish minority of 2 million). If Great Britain had not interfered by arrogantly made herself involved in affairs that did not concern her other than retain her empire status (which it lost post-WW2 thanks to her overreaching policies, take that, Britons).
When Russia decided to liberate the Balkans after the Batak massacre where thousands of Bulgarians dead. Russians managed to really kick the Ottomans' rears to the point of destroying its hegemony over the Balkans and Eastern Thrace (Konstantinopol and Odrin)... until the British intervened because they were afraid of powerful Russian allied states being established in the Balkans and of a large Slavic state after Russia (which would've been the result if the British didn't interfere and send a fleet of warships to the Sea of Marmara which stopped the Russians from taking Konstantinopol). So to this day, since the British prevented the formation of a Bulgaria that stretched from Ohrid, FYROM to Constanta which is in today's Romania and to Konstantinopol. If that had been realized, Bulgaria would not be a poor country today but a powerful country in economic and military terms next to France, the Netherlands and Belgium combined, etc. After the first Balkan War, Bulgaria fought three major wars and lost all of them. The first, the Second Balkan War had to do with all bordering countries ganging up on Bulgaria (thanks to Bulgaria's status of being the most powerful Balkan country militarily). The First World War, the Britons just had to interfere again and get involved with Balkan affairs and sent reinforcements to Greece and Serbia who were on the losing side against Bulgaria. The Second World War, the Britons and Americans bombed Sofia a couple days after Bulgaria joined the war on Germany's side (and attained greater territorial control thereafter which we lost two of three gains after the war). So for the howling that Bulgaria has no one to blame but herself, you should reexamine that statement because a lot of times, great powers like Britain have interfered in the development of a stronger Bulgaria.
And Greece? Greece in 1920s' during the Turkish War of Independence it was approaching Ankara with multiple military successes. Greece's plan depended on the supply lines the British helped flow. When Britain became terrified at Greece's military victories, it cut the supply lines that supplied Greek soldiers in Anatolia and helped the war to turn in Turkey's favor. Greece lost the war as a result. And the result of that war? The Turks continue to be among us, immigrate to Germany in large numbers and continue to be a threat to Greece and Bulgaria today. Interestingly enough, if the Britons hadn't backstabbed Greece, Greece would've recreated the Byzantine Empire and there would be a powerful Hellenic state today that isn't deep in debt (which now you can see the why behind the Britons backstabbing the Greeks as a way to retain her empire status).
I know I'm going to get a lot of flak for this post considering how most of the posters here are Anglos but hey, I'm not afraid of sharing my opinion on this matter.