Romania, which had begun the war as a neutral, sided with the Allies in August 1916, led by Ion Bratianu, after the Allies promised support for the achievement of Romania`s national unity. In October, the Romanian army was expelled from Transylvania with the help of German reinforcements, and by the end of 1916, the capital Bucharest, as well as Wallachia and Dobrudja, had fallen under the control of the Central Powers, while the Romanian government withdrew to Iași. Thompson, now head of the British military mission, had to mitigate the consequences of Romania`s surrender, and he personally oversaw the destruction of Romanian oil wells in order to deny it to Germany.  The Treaty of Bucharest was a peace treaty between Romania on the one hand and Austria-Hungary, Bulgaria, Germany and the Ottoman Empire on the other, after the stalemate after the 1916/17 campaign and the isolation of Romania after Russia`s unilateral withdrawal from World War I (see Treaty of Brest-Litovsk). It was signed on May 7, 1918 in Buftea near Bucharest. The Treaty of Bucharest of 1916 was signed between Romania and the Entente powers on 4 (Old Style)/17 (New Style) August 1916 in Bucharest.  The treaty set out the conditions under which Romania agreed to join the war on the side of the Entente, in particular the territorial promises in Austria-Hungary. The signatories undertook to keep the content of the treaty secret until a general peace was concluded. In 1915, Lieutenant-Colonel Christopher Thomson, who spoke fluent French, was sent to Bucharest as a British military attaché at Kitchener`s initiative to lead Romania to war. But when he was there, he quickly came to the conclusion that an unprepared and ill-armed Romania facing a three-front war against Austria-Hungary, Turkey and Bulgaria would be a burden and not an advantage for the Allies. This view was swept away by Whitehall and he signed a military agreement with Romania on 13 August 1916 (with premonition).  Thompson became head of the British military mission.
On the morning of August 27, 1916 (August 14, O.S.), a crown council was held at the Cotroceni Palace, convened by King Ferdinand, who decided to respect the treaty with the Entente powers. On that day, Romania declared war on Austria-Hungary and, on the same night, fired three armies of 440,000 men on the passports of the Southern and Eastern Carpathians. [Citation needed] After two years of cautious neutrality, Romania went to war in 1916 on the side of the Entente to preserve Transylvania, a region ruled by Romanian-majority Hungary and the Hungarian and German minorities. Although Bulgaria received part of northern Dobrudja, the fact that it could not annex the entire province had a strong influence on Bulgarian public opinion.  Bulgarian Prime Minister Vasil Radoslavov was forced to resign on June 20, 1918 after failing to acquire all of Dobrudja.  Nevertheless, Bulgaria continued to lobby Germany and Austria-Hungary for the annexation of the entire province, including the condominium established by the Treaty of Bucharest. Representatives of the Bulgarian Dobrudjans held a second General Assembly in Babadag on 23 September, during which they adopted a final resolution calling for the incorporation of Dobrudja into Bulgaria.  After negotiations, a protocol on the transfer of the jointly administered area in northern Dobrudja to Bulgaria was signed in Berlin on September 24, 1918 by Germany, Austria-Hungary, the Ottoman Empire and Bulgaria. In return, Bulgaria agreed to cede the left bank of the Maritsa River to Turkey.  The Protocol was seen as a desperate attempt by the Central Powers to keep Bulgaria on their side during the Vardar offensive on the Macedonian front. In the end, the agreement was short-lived: five days later, on 29 September, Bulgaria surrendered to the advancing Allied forces (see also the Thessaloniki Armistice). At the end of October, the Romanian army was expelled from Transylvania with the help of German reinforcements arriving in Transylvania to support the modest forces of Austria-Hungary.
Inevitably, this weakness continued to expose Austria-Hungary to Germany. In late 1916, the capital Bucharest fell, the government fled to Iaşi, Moldavia, and Wallachia was under the control of the Central Powers. The campaign`s blood toll was about 100,000 deaths for Romania, but it won Transylvania. Although Bulgaria received part of Northern Dobrudja, it continued to lobby in Germany and Austria-Hungary for the annexation of the entire province, including the condominium established by the Treaty of Bucharest. After negotiations, a protocol on the transfer of the jointly administered area in northern Dobrudja to Bulgaria was signed in Berlin on 25 September 1918 by Germany, Austria-Hungary, the Ottoman Empire and Bulgaria. In compensation, Bulgaria agreed to cede the left bank of the Maritsa River to Turkey. However, this agreement was short-lived, as Bulgaria had to surrender to the advance of the Allied forces after 4 days on September 29 (see also the armistice with Bulgaria). Until the outbreak of war in Europe in 1914, Romania had long disagreed with Austria-Hungary on the territorial issue – particularly with Transylvania, which was ethnically Romanian but was then part of Hungary. When Romania saw Russia`s success against Austria on the battlefields of the Eastern Front in the summer of 1916, it hoped to make an advantageous entry into the war to realize the long-cherished dreams of territorial expansion and national unity.
On August 18, 1916, the Romanian government signed a secret treaty with the Allies; According to his conditions, in the event of an Allied victory, Romania would acquire Transylvania from tisza, bukovina province from the Pruth River and the entire Banat region, all territories under Austro-Hungarian control. On 27 August, Romania fulfilled its contractual obligation by declaring war on Austria-Hungary. The degraded Falkenhayn, on the other hand, took control of Germany`s operations against Romania; He was joined by another prominent German general, August von Mackensen. By December 1916, Falkenhayn and Mackensen had led their troops to a decisive victory against Romania, invaded much of the country and occupied the capital Bucharest on December 9, 1916. Although Russian troops invaded Romania earlier the following year, the Russian army was on the verge of collapse; With the Russian Revolution that year, the rise of the Bolsheviks to power, and Russia`s subsequent exit from the war in early 1918, Romania was forced to surrender to the Central Powers in Bucharest in May, after suffering about 335,000 casualties during the war, with no civilian deaths. The Treaty of Bucharest of 1916 was signed between Romania and the Entente on the old date|27 August|1916|14 August in Bucharest. German Empire Austria-Hungary Ottoman Empire Bulgaria The military convention stipulated that Romania was to attack Austria-Hungary from the south, while Russia undertook to launch an offensive on the Austrian front to support the Romanian advance into Transylvania. In addition, the Russian high command promised to send two infantry divisions and one cavalry division to Dobruja to protect the rear of the front from a Bulgarian attack.  The French and British promised to launch an offensive on the Thessaloniki front to force Bulgaria out of the war.  When Romanian troops opened a new war front in Transylvania, British troops put pressure on Germany on the Somme and Austria weakened in the east against Russia, Emperor Wilhelm II was defeated. Germany briefly panicked and told its close confidants, “The war is lost.” However, he quickly regained perspective and strengthened Germany`s defensive position, replacing Erich von Falkenhayn on 28 August with Paul von Hindenburg as German Chief of Staff. Within two weeks, at a conference attended by the Turkish and Bulgarian leaders, William approved the creation of a Supreme War Command that effectively gave Hindenburg command of all the armies of the Central Powers during World War I.
Alexandru Marghiloman, then Prime Minister of Romania, signed the final treaty on 7 May [O.S. 25 April] 1918 at the Cotroceni Palace in Bucharest, which was ratified by the Chamber of Deputies and the Chamber of Deputies on 28 June. Senate on July 4, 1918.  However, King Ferdinand refused to sign or pronounce it. In 1917, the Romanian army recovered and, despite the disintegration of the Russian army after the February Revolution, was able to stop German attempts to break through the front. Russia`s withdrawal from the war in March 1918 with the Treaty of Brest-Litovsk left Romania alone in Eastern Europe, and in May 1918 a peace treaty was negotiated between Romania and the Central Powers (Treaty of Bucharest (1918)). .