我自己想到的交战情况就这些了
1914年秋与协约国签订协约，加入一战
1916.8.27分三路出击匈牙利
1916.10.9退入山地防御
1916.12.1放弃首都，战略转移
1916.12.4全境沦陷，退到黑海

羅馬尼亞戰役是指第一次世界大戰期間在羅馬尼亞進行的戰爭，交戰雙方是羅馬尼亞王國俄羅斯帝國，以及同盟國。一戰開始之後，羅馬尼亞在1916年8月7日加入協約國。之後羅馬尼亞遭到同盟國軍隊的全面攻擊。1916年12月6日，同盟國軍隊攻占布加勒斯特，國土大部分都被同盟國佔領。1918年5月7日，羅馬尼亞正式投降。但在戰後由於協約國取得一戰的最後勝利，羅馬尼亞成為一戰的戰勝國。

The Romanian campaign was part of the Balkan theatre of World War I, with Romania and Russia allied against the armies of the Central Powers. Fighting took place from August 1916 to December 1917 across most of present-day Romania, including Transylvania, which was part of the Austro-Hungarian Empire at the time, as well as southern Dobruja, which is currently part of Bulgaria.
Romania entered the war in an attempt to seize Transylvania, a region with significant Romanian population, from the Austro-Hungarian Empire. Despite initial successes, the Romanian forces (aided by Russia) suffered several setbacks, and by the end of 1916 only Moldavia remained under Allied control. After several defensive victories in 1917, with Russia's withdrawal from the war following the October Revolution, Romania, almost completely surrounded by the Central Powers, was also forced to drop out of the war; it signed the Treaty of Bucharest with the Central Powers in May 1918. On 10 November 1918, just one day before the German armistice and after all the other Central Powers had already capitulated, Romania re-entered the war. By then, about 220,000 Romanian soldiers had been killed, about 6% of total Entente military deaths.
（英文wiki讲得很详细，肯得动的就去肯吧，词条Romania during wwi）