Editing Ion Antonescu (section)

===World War I===
[[File:1916 - Generalul Prezan, Olga Prezan, Olga Prezan, o rudă, maior Ion Antonescu, căpitan M. Tomaide - văr lui Antonescu.PNG|thumb|upright=1.2|left|Major Ion Antonescu (second from the right) with General [[Constantin Prezan]] and his wife Olga Prezan (first and second from the left, respectively), 1916]]
{{Fascism in Romania|people}}
[[File:Ofițerii Secția Operațiuni Marele Cartier General Român 1918.jpg|thumb|Antonescu (''bottom row, centre'') with the other officers of the Section "Operations" of the wartime General Staff (''Marele Cartier General''), end of March 1918]]
After 1916, when Romania entered World War I on the [[Allies of World War I|Allied]] side, Ion Antonescu acted as chief of staff for General [[Constantin Prezan]].<ref name=d37/> When enemy troops crossed the mountains from [[Transylvania]] into [[Wallachia]], Antonescu was ordered to design a defence plan for Bucharest.<ref name=d37/>

The Romanian royal court, army, and administration were subsequently forced to retreat into [[Moldavia]]. Antonescu took part in an important decision involving defensive efforts, an unusual promotion which probably stoked his ambitions.<ref name=r1/> In December, as Prezan became the [[Chief of the Romanian General Staff|Chief of the General Staff]], Antonescu, who was by now a major, was named the head of operations, being involved in the defence of Moldavia. He contributed to the tactics used during the [[Battle of Mărășești]] (July–August 1917), when Romanians under General [[Eremia Grigorescu]] managed to stop the advance of German forces under the command of Field Marshal [[August von Mackensen]].<ref>Deletant, pp. 37–38</ref> Being described as "a talented if prickly individual",<ref>Prit Buttar, [[Bloomsbury Publishing]], 22 September 2016, ''Russia's Last Gasp: The Eastern Front 1916–17'', p. 320</ref> Antonescu lived in Prezan's proximity for the remainder of the war and influenced his decisions.<ref name=d38>Deletant, p. 38</ref> Such was the influence of Antonescu on General Prezan that General [[Alexandru Averescu]] used the formula "Prezan (Antonescu)" in his memoirs to denote Prezan's plans and actions.<ref>Larry Watts, Eastern European Monographs, 1993, ''Romanian Cassandra'', p. 43</ref>

That autumn, Romania's main ally, the [[Russian Provisional Government]], left the conflict. Its successor, [[Russian Soviet Federative Socialist Republic|Bolshevik Russia]], made peace with the [[Central Powers]], leaving Romania the only enemy of the Central Powers on the [[Eastern Front (World War I)|Eastern Front]]. In these conditions, the Romanian government made its own [[Treaty of Bucharest (1918)|peace treaty with the Central Powers]]. Romania broke the treaty later in the year, on the grounds that King Ferdinand I had not signed it. During the interval, Antonescu, who viewed the separate peace as "the most rational solution," was assigned command over a cavalry regiment.<ref name=d38/> The renewed offensive played a part in ensuring the [[union of Transylvania with Romania]]. After the war, Antonescu's merits as an operations officer were noticed by, among others, politician [[Ion G. Duca]], who wrote that "his [Antonescu's] intelligence, skill and activity, brought credit on himself and invaluable service to the country."<ref name=d38/> Another event occurring late in the war is also credited with having played a major part in Antonescu's life: in 1918, Crown Prince [[Carol II of Romania|Carol]] (the future King Carol II) left his army posting to marry a commoner. This outraged Antonescu, who developed enduring contempt for the future king.<ref name=r1/>