1. Antiquity's fragments: treaty practice and diplomatic immunity in the ancient Near East, Greece (ius fetiale, amphyctionic councils) and India (Kautilya's inter-state rules) — rules of inter-polity conduct, but no system of interstate law among sovereign equals.
2. The natural-law era — Grotius (1583–1645): the Thirty Years' War's wreckage produced Hugo Grotius, De Jure Belli ac Pacis (1625) — the "father of international law" law between states grounded in natural reason and the jus gentium, binding even in war (jus in bello). Precursors: Vitoria (the rights of the Indians), Gentilis (the secular lawyer's law), Suárez.
3. Westphalia (1648): the sovereignty-settlement — a Europe of territorially sovereign, legally equal states — international law's political matrix.
4. The positivist 18th–19th centuries: Vattel (The Law of Nations, 1758 — sovereign equality's classic); the Congress of Vienna (1815) codifying diplomacy's ranks and the slave-trade's suppression beginnings; the Hague Conferences (1899, 1907 — peaceful settlement, the laws of war, the Permanent Court of Arbitration); positivism's method — law as state consent, not natural reason.
5. The 20th century — institutionalization and universalization: the League of Nations (1919) and the PCIJ; the United Nations (1945) — the Charter's force-prohibition and collective security; the ICJ; the Nuremberg/Tokyo tribunals (individual criminal responsibility); the decolonization wave universalizing the law (the "family of nations" becomes global — Nepal's UN admission, 1955, a chapter of this story); the law's explosion — sea, space, environment, trade, human rights (UDHR 1948; ICCPR/ICESCR 1966), international criminal justice (the ad hoc tribunals; the ICC, 1998/2002 — Nepal the first South Asian state party, joining in 2006–07).
6. Contemporary phase: globalization's legalization (WTO's binding dispute settlement, 1995); the fragmentation debates (self-contained regimes, lex specialis); non-state actors (terrorist networks, MNCs); cyber and AI's new frontiers; and the return of great-power strain on the Charter order (Unit 1 of IR) — international law's permanent condition: tested, adapted, still standing.