Sima had previously served briefly as State Secretary of Education under Gheorghe Tătărescu in 1940, and as a short-lived Minister of Religion and Arts in the government of Ion Gigurtu.

[13] Prior to his ascension to leadership, tension had built significantly both within the organization and country-wide following a series of assassinations of Iron Guard members, including of Codreanu (who was killed by order of King Carol II).

[9]: 141–43  On 4 July 1940, he joined the cabinet of Ion Gigurtu as the undersecretary of state in the Ministry of Public Education, as well as Minister of Religion and Arts,[17] alongside two other Iron Guard members.

[20] Beginning in August 1940, prior to this secession, the Iron Guard faction controlled by Sima began to organize for a coup against King Carol II in reaction to the concession of Northern Transylvania.

Although the coup was unsuccessful, it spurred a number of protests against Carol II, and by 4 September the King had appointed General Ion Antonescu to the position of Prime Minister, thus halting the uprising.

[9]: 158–61 In September 1940, Carol II abdicated and the Iron Guard entered a tense political alliance with General Ion Antonescu, forming what was proclaimed the National Legionary State.

[21] At that point, Sima was able to officially return from exile and rise to power as deputy prime minister in the new government, as well as resume his activities as leader of the Iron Guard in Romania.

[22] Tension and issues began to arise in Romania under the Sima-Antonescu partnership, and Antonescu became increasingly frustrated with the Iron Guard, telling Sima that it was now "...time for order and legality" and that Legionnaires would "not [be] allowed to demand audiences with the Ministers whenever they want.

[24][25] Sima responded to dissent within the Iron Guard by placing a number of prominent Legionnaires under house arrest, including Corneliu Zelea Codreanu's brothers and father.

[9]: 175–6  Alongside a group of dissatisfied Legionnaires, the senior Codreanu occupied the Iron Guard's Bucharest headquarters, the Casa Verde, and attempted a putsch.

[26] In the Bucharest pogrom, staged alongside this power struggle, Iron Guardists destroyed synagogues, vandalized and ransacked Jewish homes and stores,[27] and killed and tortured 121 Jews (as well as an additional 30 in smaller towns, specifically in Ploiești and Constanța).

[9]: 199 While interned at Buchenwald, Sima was faced with the dissent of several groups of Legionnaires who distanced themselves from his policies, stating that they did not approve of the way in which he had run the country and the movement, and who began to appeal to the German supervisors for distinctions to be made in their case.

"[40] Legionnaires increasingly began to blame Sima's leadership of the Iron Guard for the death of Codreanu, citing his previous actions as commander in 1938 as "terroristic" and "tumultuous".

By 1943, the Iron Guard — now in exile in Rostock, Germany — had split into at least three distinct groups with separate leadership, not including the Legionnaires who considered Sima their legitimate leader.

[50] The publication of these accusations in Vatra, alongside other political tensions, caused the resignation of a number of members of the Guard, as well as the foundation of a new faction named "Moța-Marin" under the leadership of Ovidiu Găină.

[50] Central Intelligence Agency documents claim that Sima, in light of these allegations, had originally planned to end his career by parachuting into Romania,[51][52] where he had previously been sentenced to death following two separate trials.

[60] This adoption of a new image was, in part, successful — beginning in 1949, the United States helped to fund NATO missions to parachute Iron Guard members into Romania in an attempt to undermine the socialist government.

[63] After the death of his wife Elvira in 1974, Sima resided with fellow exiled Iron Guard member Gheorghe Costea in Madrid, and the two used funds from publishing and donations as income.