He spent the early years of World War I in France, appointed to the staff of Joseph Joffre, but returned in time to participate in the Romanian offensive of 1916.

Zadik withdrew from active duty and took administrative positions, including one at the Aircraft Construction Enterprise, while also serving as vice president of Cultul Eroilor society in the late 1920s.

[13] By December, his son Grigore had been evacuated with the entire Dealu army school to Iași, and faced the prospect of being moved to safety in the Russian Empire.

[22] During the defense of Moldavia, Zadik helped his troops achieve victory in the Battle of Mărășești, though he later credited success to "the Romanian peasant set out to defend his ancestral lands".

[24] While serving as a Secretary in the Ministry of War Ammunition (from September 1), Zadik held a command position in the First Battle of Oituz, and became an Officer of the Order of the Crown (he would receive its Grand Cross in 1919).

[25] Grigore Zadik saw action with the Romanian Air Force (Balloon Corps),[17] despite being underage; as reported by the General, his son's missions were his only cause for worry during that stage of war.

In autumn 1918, after the Austrian governor of the Duchy of Bukovina, Josef Graf von Ezdorf, refused a request by Iancu Flondor to cede power, Zadik led the troops who occupied the province.

[33] Literary historian Ion Filipciuc believes that, while the brigands in such descriptions have generally been taken for Austrian Sich Riflemen under Archduke Wilhelm of Austria, they were in fact "Ukrainian deserters and Bolsheviks", who numbered in the hundreds, and who only had immediate goals such as robbery.

[35] However, in a letter he sent to Alexandru Tzigara-Samurcaș, Marghiloman argued that he was acting specifically against Austrian rule, and confessed that Zadik was to march on Cernăuți, the Bukovinian capital.

Their exact orders were to act as if on a regular campaign, directed against "brigands" (răufăcători), but without any forced requisitioning; troops were to return to their headquarters once this mission was declared accomplished.

[45] He stationed his force for a days-long rest about 60 kilometers outside the city; Lazăr traveled there to meet him: "I asked him to make his entry, for the population had been out in the streets for three days, waiting for him to arrive.

[46] In their speeches, both Flondor and Zadik referenced "Greater Romania"—the latter also paid homage to Grigore Ghica, who had tried to oppose Bukovina's occupation in 1774, and had "lost his head" as a result.

Both speeches were weak and poorly recited: either speaker lost his train of thought again and again, could no longer recall phrases they had learned by heart, and took such pauses that under normal circumstances would have been embarrassing.

[52] Within days of his Cernăuți entry, the Romanian General Staff ordered Zadik to occupy the entire Bukovina, including its Ukrainian-majority northern half.

[53] As head of the General Staff, Constantin Prezan personally cleared Zadik for this expedition, which went against the terms of the November Armistice; during his advance, he also routed the Sich Riflemen, who withdrew from northern Bukovina, and captured Archduke Wilhelm.

[54] The operation, fully accomplished on November 21, was largely without bloodshed—one exception occurred during the advance on Luzhany, when the "Dragoș" detachment was engaged in a skirmish that resulted in deaths on both sides.

[61] On May 28, he met with Polish General Franciszek Kraliczek-Krajowski, agreeing to form a joint military command and a civilian government, both based in Kolomyia.

His final report to Petala included a request to have the Polish 4th Rifle Division moved out of Cernăuți (where it was allegedly causing damages) and into Pokuttia.

He then oversaw the terms of the withdrawal with his Polish counterparts, Wacław Iwaszkiewicz-Rudoszański and Robert Lamezan de Salins; discussions took place in Lemberg, but the outcome was postponed by more urgent developments in the parallel Hungarian–Romanian War.

[72] Zadik continued to be well regarded by the Bukovina Jews and Germans, with the newspaper Das Volk describing him as an "honorable defender and supporter" of the ethnic minorities.

[73] On December 14, Zadik was at Cernăuți, attending a parastas service held by the Romanian Orthodox Church in memory of Bukovinians killed in action throughout the war.

This drew controversy in Romania, as creating a precedent for generals legislating against Parliament; as noted by the newspaper Adevărul, his ruling was also a way to bypass the anti-censorship laws advanced by the National Peasants' Party and the Maniu cabinet.

[72] In 1935 he was one of the inaugural holders of the Order of Ferdinand I (as Grand Officer), also being recognized as an honorary citizen of Cernăuți in autumn 1937 (though some reports suggest that this distinction was bestowed upon him in 1918).

[86] Of Iacob's progeny, Grigore took high positions in the military, serving as Ion Antonescu's aide on mission to the League of Nations (1936); a Major in 1937, he spent the years 1937–1939 training with France's 11th Artillery Regiment, and, like his father, was inducted into the Legion of Honor.

[17] With his training in both artillery and aviation, he commanded and organized Bucharest's anti-aircraft defense during the early stages of World War II, when Romania was aligned with the Axis Powers (1940–1942).

[17] In 1967, the General recalled that he approved of the anti-Axis coup of August 1944;[88] in its immediate aftermath, Grigore Zadik served as a liaison between the Romanian Army and Fyodor Tolbukhin's 4th Ukrainian Front.

[97] In old age, Iacob Zadik donated his memorabilia to the National Military Museum, and "three hundred of my valuable books, as well as forty-four music sheets—old songs and romanzas" to the Romanian Academy.

[72] Scînteia reporters visited him and his son at their home during the legislative election of March 1969, alongside a team carrying the mobile ballot box.

They quoted Zadik Sr as saying that his interest as a former soldier was in supporting world peace on the basis of non-interventionism; his son added that they had both been impressed by Ceaușescu's "extremely realistic foreign policy, with its rooting in truly reasonable principles".

[104] General Zadik was formally commemorated by the Armenian community in Romania, represented by Varujan Vosganian and Gregorian bishop Tadev Hakobyan-Muradyan, with a special service held at Bellu on November 27, 2018.