Short answers, pulled from the story.
The Romanian parliament raised the country to the status of a kingdom on the 15th of March 1881, and Carol I was crowned king on the 10th of May that year. The kingdom lasted until the 30th of December 1947, when King Michael I abdicated and the Romanian People's Republic was proclaimed.
The first king of Romania was Carol I, born Karl Eitel Friedrich Zephyrinus Ludwig von Hohenzollern-Sigmaringen, a German prince and Prussian officer. He was appointed Prince of Romania in 1866 after the forced abdication of Alexandru Ioan Cuza, immediately adopted the Romanian spelling of his name, and was crowned king in 1881.
Romania declared independence on the 9th of May 1877, at the start of the Russo-Turkish War of 1877-1878, known locally as the Romanian War of Independence. The Treaty of Berlin in 1878 formally recognized Romanian sovereignty. In exchange for gaining Northern Dobruja, Romania was forced to cede the southern part of Bessarabia to Russia.
After World War I, Romania received Transylvania, part of Banat, Bessarabia, and Bukovina through the Paris Peace Conference, the Treaty of Saint-Germain in 1919, and the Treaty of Trianon in 1920. By 1920, Romania was more than twice the size it had been in 1914, a period referred to as Greater Romania.
The Iron Guard was a quasi-mystical fascist movement that exploited nationalist sentiment, fear of communism, and antisemitism. It embraced political assassination, killing Prime Minister Ion Duca in December 1933 and Prime Minister Armand Calinescu in September 1939. Its leader Corneliu Zelea Codreanu was arrested by King Carol II in April 1938 and killed on the night of the 29th-the 30th of November 1938 while allegedly attempting to escape prison.
In 1944, King Michael led a coup against dictator Ion Antonescu, switching Romania from the Axis to the Allied side and recovering Northern Transylvania. Soviet influence over postwar governments proved decisive, and on the 30th of December 1947 King Michael abdicated. The Romanian Parliament proclaimed the Romanian People's Republic, making Romania a Soviet satellite state.
The first oil refinery in the world was built at Ploiesti, Romania, in 1857. By the late 1930s Romania had become one of the top crude oil exporters globally, producing 6.6 million tons of crude oil in 1938 alone. This made Romania's oil resources a significant factor in attracting German and Italian interest in the country during World War II.