On 18 September 96, Domitian was assassinated in a palace conspiracy involving members of the Praetorian Guard and several of his freedmen. On the same day, Nerva was declared emperor by the Roman Senate. As the new ruler of the Roman Empire, he vowed to restore liberties that had been curtailed during the autocratic government of Domitian.

The defeat of the superior fleet of Licinius in the Battle of the Hellespont by Crispus, Constantine's eldest son and Caesar, compelled his withdrawal to Bithynia, where the last stand was made; the Battle of Chrysopolis, near Chalcedon (18 September), resulted in Licinius' final submission.

844 Damascus earthquake occurred on September 18, 844, in Abbasid Caliphate (now Syria), there were an estimated 50,000 deaths.

The Austro-Russian–Turkish War (1735–1739), which was ended by the Treaty of Belgrade in 1739, resulted in the Ottoman recovery of northern Bosnia, Habsburg Serbia (including Belgrade), Oltenia, and the southern parts of the Banat of Temeswar; but the Empire lost the port of Azov, north of the Crimean Peninsula, to the Russians. After this treaty, the Ottoman Empire was able to enjoy a generation of peace, as Austria and Russia were forced to deal with the rise of Prussia.

The British Parliament passed the Third Home Rule Act on 18 September 1914 with an amending Bill for the partition of Ireland introduced by Ulster Unionist MPs, but the Act's implementation was immediately postponed by the Suspensory Act 1914 due to the outbreak of the First World War in the previous month. The majority of nationalists followed their IPP leaders and John Redmond's call to support Britain and the Allied war effort in Irish regiments of the New British Army, the intention being to ensure the commencement of Home Rule after the war.