4th January » Constantine Hangerli arrives in Bucharest, Wallachia, as its new Prince of Wallachia called Prince, invested by the Ottoman Empire.
10th February » Louis Alexandre Berthier invades Rome, proclaims a Roman Republic (18th century) named Roman Republic on February 15 and then on February 20 takes Pope Pius VI prisoner.
15th February » The Roman Republic (18th century) or Roman Republic is proclaimed after Louis Alexandre Berthier, a general of Napoleon I of France or Napoleon, had invaded the city of Rome five days earlier
20th February » Louis Alexandre Berthier removes Pope Pius VI from power.
7th April » The Mississippi Territory is organized from disputed territory claimed by both the United States and Spain. It is expanded in 1804 and again in 1812.
24th May » The Irish Rebellion of 1798 led by the Society of the United Irishmen known as United Irishmen against Kingdom of Great Britain or British rule begins.
25th May » Irish Rebellion of 1798 United Irishmen Rebellion: The Carnew massacre, Massacre of Dunlavin Green Dunlavin massacre and Battle of Carlow Carlow massacre take place.
27th May » The Battle of Oulart Hill takes place in Wexford, Ireland.
29th May » Irish Rebellion of 1798 United Irishmen Rebellion: Between 300 and 500 Society of United Irishmen United Irishmen Gibbet Rath massacre are massacred by the British Army in County Kildare, Ireland.
5th June » Battle of New Ross (1798) or The Battle of New Ross: The attempt to spread the Irish Rebellion of 1798 e.g United Irish Rebellion into Munster is defeated.
9th June » Irish Rebellion of 1798: Battle of Arklow and Battle of Saintfield.
12th June » Irish Rebellion of 1798: Battle of Ballynahinch.
21st June » Irish Rebellion of 1798: The British Army defeats Irish rebels at the Battle of Vinegar Hill.
7th July » Quasi-War: the United States Congress named U.S. Congress rescinds treaties with France sparking the "war".
11th July » The United States Marine Corps is re-established; they had been disbanded after the American Revolutionary War.
14th July » The Alien and Sedition Acts Sedition Act becomes United States law law in the United States making it a federal crime to write, publish, or utter false or malicious statements about the Federal government of the United States United States government.
1st August » French Revolutionary Wars: Battle of the Nile known as Battle of the Nile (Battle of Aboukir Bay) Battle begins when a British fleet engages the French Revolutionary Navy fleet in an unusual night action.
2nd August » French Revolutionary Wars: the Battle of the Nile concludes in a British victory.
17th August » The Vietnamese Roman Catholics report a Marian apparition in Quảng Trị, an event which is called Lady of La Vang.
31st August » Irish Rebellion of 1798: Irish rebels, with French assistance, establish the short-lived Republic of Connacht.
5th September » Conscription is made mandatory in France by the Jourdan law.
4th November » Beginning of the Siege of Corfu (1798–99) called Russo-Ottoman siege of Corfu.