This statistic shows the total population of the Kingdom of Serbia from 1834 to 1910. In the early nineteenth century Serbia was under the control of the Ottoman Empire, and was granted de facto independence from the Ottomans in 1817 (although the Ottomans still occupied Belgrade until 1867). With the weakening of the Ottoman Empire in the 1800s, and the expansion of other European powers such as Austria and Russia, Serbia's borders changed frequently and over time it gained stability and international acceptance as a new independent state. The population given here is not of the modern-day area of Serbia, but rather the nineteenth century Kingdom of Serbia, which was significantly smaller.

In 1834, the population of the Kingdom of Serbia was just 678 thousand people, although there were many ethnic Serbs living outside these borders under the rule of other kingdoms. The population then grew rather steadily to 1.35 million in 1874, before it grows to 1.9 million in 1884. This huge jump in the population is a result of the acquisition of new territory from the Ottomans, which added over 300,000 people to the Kingdom, and the new data also included military personnel, which was not included in the previous entries.

From 1884 onwards the population continues to grow, and it reaches 2.9 million people by 1910, which is the final collection of data before the First World War. World War I began on July 28th 1914 when Austria-Hungary declared war on Serbia in retaliation for the assassination of Franz Ferdinand by a Bosnian Serb, Gavrilo Princip, in Sarajevo one month before. By the end of the war as many as 1.3 million Serbs died as a direct result of the conflict, which is the highest percentage of any overall population involved in the war, and almost sixty percent of all Serbian men died.

Albania, then known as Rumelia, was a province of the Ottoman Empire from the fifteenth century until it declared it's independence in 1912. Following a series of unsuccessful uprisings and brief occupations from nearby Serbia and Greece, Albania finally claimed its independence on November 28, 1912; however the Conference of London in 1913 then set the borders of the former-Ottoman states in Southern Europe, which left many ethnic Albanians living in other neighboring states, particularly Serbia (and what is now Kosovo). The newly-formed Albanian state collapsed in the wake of the First World War, and was controlled in parts by Greece, Italy and Serbia. The Paris Conference then established an independent Albanian state, which led to a period of political and economic turmoil that lasted until Italy's annexation of the region in 1939, during the Second World War. It is estimated that just under 3 percent of Albania's population perished as a direct result of the war, as Albania became the main theater for the Axis Powers' war against Greece. Italy then surrendered control of the area to Germany in 1943, and after the war ended in 1945, Albania became a Yugoslav satellite state and remained behind the Iron Curtain until it's collapse in the 1990s. Steady growth during the communist era From the war's end onwards, Albania's population enjoyed steady growth and almost tripled by 1990. Throughout this time, Albania underwent a series of political allegiances; first as a Yugoslav and then Soviet satellite states, but then became an important actor in the Sino-Soviet split, eventually siding with China in the 1960s. Gradually, Albania transitioned into a more isolationist and independent country in in the 1970s, and slowly adopted some more democratic practices. The total population surpassed two million people in the late 1960s, and three million in the late 1980s, but then a dramatic change in population growth occurred in the 1990s, as communism in Europe came to an end. Immediate decline following communism's end Increased freedom of movement, improved access to contraception and major lifestyle changes caused the population to fall into decline. The population did increase in the late 90s, despite a civil war in the first half of 1997 (in which over 2 thousand people died) sparked by a failure of the financial system in Albania. The Albanian Army was also involved in the war in neighboring Kosovo between 1998 and 1999. The 2000s brought about further decline, and the population is just 2.9 million in 2020, a decline of approximately 400,000 people in thirty years. Albania has been a candidate for accession to the EU since 2014, and membership would bring further change to the country.

Bulgaria, with the help of the Russian Empire, achieved independence from the Ottoman Empire in 1878. In the decades before independence, Bulgaria's population had remained between 2.2 and 2.8 million people, and growth was much slower then the following century. Although most at the time assumed that it would become a Russian ally, Bulgaria defied the expectations and aligned itself with the western powers, and developed into a modern European state by the turn in the late 1800s. Bulgaria at war In the early twentieth century Bulgaria was involved in both World Wars, as well as two Balkan Wars. The Balkan states were unhappy with the borders assigned to them by the western powers, and instead wanted to re-draw them based on the dispersal of ethnic groups. This led to the first Balkan War in 1912, which saw Bulgaria fight alongside Greece and Serbia against the Ottomans. Bulgaria fought the second Balkan War on all sides, this time against Greece, Serbia, Romania and the Ottomans, as the dispute over borders continued. Bulgaria was defeated this time, and sustained heavy casualties, amassing in 58 thousand fatalities and over 100 thousand wounded in the two wars.

In the First World War, Bulgaria remained neutral at first, in order to recover from the previous wars, but then aligned itself with the Central powers in 1915, and played a vital role in maintaining their control in the Balkans. While Bulgaria was initially successful, its allies weakened as the war progressed, and then Bulgaria eventually succumbed to Allied forces and surrendered in 1918, with almost 200 thousand Bulgarians dying as a result of the war. The interwar years was a period of political and economic turmoil, and when control was re-established, Bulgaria was then able to maintain it's neutrality throughout most of the Second World War, (although there was some conflict and bombings in certain areas). Rise and fall of communism After the war, Bulgaria became a communist state, and life became harsh for the civil population there until the late 1950s when the standard of living rose again. In the late 1980s, like many Eastern European countries, Bulgaria experienced economic decline as the communist system began to collapse. Political failures also contributed to this, and approximately 300 thousand Bulgarian Turks migrated to Turkey, greatly weakening the agricultural economy. This trend of mass migration abroad continued after the fall of the iron curtain, as well as the rise of unemployment. Bulgaria reached it's peak population size in 1985 at 8.98 million inhabitants, but then the number decreases each year, and is expected to be 6.94 million in 2020. This drop in population size has been attributed to the economic collapse at the end of communism in Eastern Europe, causing many to leave the country in search of work elsewhere. Bulgaria also has one of the lowest fertility rates in the world, with 8.7 births per 1,000 people per year (in 2018).