World War I(1916–1919)

Romania's initial invasion of Transylvania was first successful, then Falkenhayn's counterattack pushed them back through the passes.

Catastrophic defeat in Dobruja. The entire garrison was killed or captured — 28,000 Romanian casualties.

Ambitious Danube crossing created a bridgehead before a storm and Dobruja collapse forced withdrawal.

Romanian defenders used mountain terrain to neutralize Central Powers artillery, limiting the enemy advance to 7 km.

Gen. Dragalina was mortally wounded leading a counterattack. Despite initial success, the valley was lost to superior German forces.

Romanian and Serbian forces held the Cerna valley against repeated Central Powers attacks in difficult mountain terrain.

Romanian forces attempted to halt the German advance on the Olt river line but were outflanked.

Romania's last major counteroffensive briefly achieved local successes before Mackensen breached the line and Bucharest fell on Dec 6.

After defeats on multiple fronts, Bucharest fell. The government fled to Iași in Moldavia.

Bulgarian forces captured Bazargic (modern Dobrich) in southern Dobruja. Romanian forces retreated northward after failing to hold the city against numerically superior Bulgarian forces executing a double envelopment.

Allied counter-offensive against the Cobadin defensive line failed. Romanian-Russian forces could not break through Bulgarian fortifications defending the ridge overlooking Dobruja, and withdrew after a day of inconclusive fighting.

Second Allied attempt to break the Cobadin line failed. Mackensen assumed overall command and launched a counter-offensive that drove allied forces north of the Cernavoda–Constanța railway. Constanța fell October 22, depriving Romania of its Black Sea supply line.

Falkenhayn's counter-offensive struck the Romanian 1st Army south of Sibiu. After four days of heavy fighting in mountain foothills, Romanian forces retreated through Carpathian passes back into Wallachia.

Romanian forces held Oituz Pass against a determined Central Powers attempt to break through into Moldavia from the west. Six days of fierce mountain fighting ended with the attackers withdrawing without achieving their objective.

Second German attempt to force Oituz Pass with doubled reinforcements was also repulsed after nine days of heavy mountain fighting in snow and extreme cold. Grigorescu's defense became legendary in Romanian military history.

German forces breached Vulcan Pass defenses in the Jiu Valley. General Dragalina was mortally wounded on November 11. With command disrupted, Romanian forces could not hold, and the retreat through Oltenia began.

Romanian forces held the Bran Pass area against Falkenhayn's attempt to break through at Dragoslavele for eleven days. After sustained fighting, the German advance was halted and they withdrew to regroup.

First Romanian offensive victory of 1917. The French-reformed army proved itself battle-ready.

"Pe aici nu se trece!" (None shall pass!) — Romania's greatest WWI battle. The German advance was halted.

Fierce fighting in the Oituz Valley blocked an enemy flanking attempt toward Moldavia.

Romanian forces crossed into Bessarabia, fought at Bender, and occupied Chișinău. Led to the union of Bessarabia with Romania on Apr 9, 1918.

Romanian forces advanced into Transylvania post-Armistice, entering Cluj on December 24.

After the Bolshevik Revolution disintegrated the Russian army on the Romanian front, the 9th and 10th Divisions of the Russian 4th Siberian Corps attempted to force passage through Galați toward Bessarabia, threatening to spread Bolshevik revolution. When Commander Niculescu-Rizea refused their ultimatum, Russian batteries bombarded the city for 15 hours. Romania executed a coordinated joint-arms counterattack — the first in Romanian military history — using land, naval, and air assets simultaneously. Four torpedo boats struck the Russian flanks from the Danube while the 8th Brigade assaulted from the north. The 12,000 Russians capitulated and were disarmed and escorted across the Prut.

After the Hungarian Red Army's northern offensive into Slovakia stalled, Mărdarescu launched a coordinated counter-offensive that swept through Carei, Oradea, and Debrecen, driving Hungarian forces back to the Tisza by May 1.

Romanian forces repelled the Hungarian attack across the Tisza, then crossed the river in a decisive counteroffensive.

Romanian forces crossed the Tisza Jul 29–30; the Hungarian Red Army disintegrated and Béla Kun fled. Budapest entered Aug 3–4.