Present day Nepal was divided into more than 50 small states before the unification. Great King Prithvi Narayan Shah (1723-1775) established the base of Nepal as a united country from his small Gorkha Kingdom. After him, wife of his first son Queen Rajendra Laxmi and his second son Bahadur Shah further extended the border of Nepal all the way to Bhutan to the east and Punjab to the west.
1723 Jan : Birth of the Great King Prithvi Narayan Shah
1743 Sep 25: ascended to the throne of Kingdom of Gorkha. Boundary of Gorkha were Trisuli River in the east bordering Nepal, Marsyangdi River in the west bordering Lamjung Kingdom and Tibet in the North.
1744 : First attack on Nuwakot, failed.
After that he visited Kashi (Benaras), Changed his gotra from Bhardwaj to Kashyap, Studied political and economic condition of East India Company and brought war weapons from there.
Then he made peace alliance with Kingdom of Lamjung, the traditional enemy of Gorkha. Also made agreements with Kaski, Tanahun and Palpa.
1744 Sep 26 : Second Attack on Nuwakot and Conquered.
Then attacked Belokot and conquered.
Then he took possession of all strategic points in the hills surrounding the Kathmandu Valley including Naddum, Mahadev Pokhari, Dahachowk, Ippa, Malta, Siranchowk, etc.
Lamjung with other small chaubisi kingdoms attacked Gorkha but defeated.
He called the King of Tanahun to the bank of Trishuli for friendship meeting and captured. So, Kingdom of Tanahun also annexed to the Gorkha.
1756 : Occupation of the Kuti Pass, stopped the Kathmandu's trade with Tibet.
1757 Dec 4 : First attack on Kirtipur but defeated, General 'Kalu Pandey' killed
1762 Aug 21 : Attacked on Makwanpur and conquered.
1763: Defeated of the Muslim forces of Mir Kasim, King of Bengal who had came to help Makwanpur by the request of King Digbandhan Sen.
1764 Sep 16 : Second attack on Kirtupur again defeated
1766 Mar 17 :Third attack on Kirtupur and conquered
1767 : Defeated British forces on the command of Captain Kinloch who had come to help Kathmandu.
1768 Sep 26: Attacked and conquered Kathmandu
1768 Oct 6 : Attacked and conquered Patan (Lalitpur)
1769 Nov 12 : Attacked and conquered Bhaktapur
1773 : Conquered Chaudandi Kingdom [Udayapur]
1774: Conquered Vijayapur Kingdom
1775 Jan 11 : Great King Prithvi Narayan Shah died at the age of 52. By then the area of Nepal was almost half of today covering all eastern and central region and parts of western region of today.
1775 Jan 12 : His son Pratap Singh Shah ascended to the throne. But died early on 1777 Nov 17.
1777 Nov 17 : 2 and half years old son of Pratap Singh 'Rana Bahadur Shah' became King. His mother Queen Rajendra Rajya Laxmi Devi ruled on his name until 1785 July 13.
1779 : Attacked and conquered Tanahun.
1781 : Palpa attacked Gorkha with the help of Chaubisi forces but defeated again
1782 : Lamjung and Tanahun annexed to Nepal.
1784 July : Attacked Parbat and conquered.
After that Bhirkot, Rishing Satahun, Garahun, Dhor, Paiya and Charikot were annexed to Nepal
1785 July : Bahadur Shah became regent to the baby king after Queen Rajendra Laxmi died.
He married the daughter of King of Palpa Mahadatta Sen and had friendly relationship.
Then he invaded Gulmi, Khanchi, Dhurkot, Kushma and Baglung, Piuthan, Dang, Jajarkot, Musikot, Dailekh, Achham and Doti one after another. By 1790 A.D. the western border of Nepal reached up to the Mahakali river, the present day border.
1789 : conquered Illam and Sikkim
1791 : conquered Kumaun and Garhwal
1790 - 91: Nepal attacked and conquered Tibet
1792-93 : China attacked Nepal in support of Tibet. Nepal forced back to its original border.
1814 : British East India Company declared war on Nepal.
1816 March 14 : Sugaili Treaty ratified (signed 1815 Dec 2). Nepal lost all lands beyond Mechi and Kali River and All terai beteen Koshi and Mahakali [Sugauli Treaty Article 3 (i) (ii) (iii)]
1816 Dec 8 : Complementary treaty signed which gave back Nepal's lost Terai lands except the one between Kali and Rapti.
1857 Dec 10 : Jung Bahadur Rana send 15,000 troops to crush Sepoy Munity in British India. British Government in India gave back the Terai plains between Rapti and Mahakali. Which includes present day 4 westernmost terai districts Banke, Bardiya, Kailali & Kanchanpur.