Old diplomacy (the classical European system, 1648–1914): secretive (negotiations behind closed doors; the Congress of Vienna's (1815) professional discretion), bilateral and Euro-centric (the great powers' concert), aristocratic (a diplomatic corps of nobles with shared culture and protocol — French as the professional language, ranks codified by the 1815 Regulation of Vienna: ambassadors, envoys, ministers resident — the lineage of today's VCDR classes), professional-craft oriented (the resident embassy's continuous ministrations), and exclusivist (legitimacy over self-determination; small states and non-European polities outside the club).
New diplomacy (post-1919, Wilson's Fourteen Points as manifesto): open ("open covenants openly arrived at" — the aspiration, never the practice), multilateral and conference-based (the League of Nations, then the UN system: standing multilateral machinery), parliamentaryand summitry (assemblies and heads-of-state summits — from Versailles to the G20), democratized and global (universal membership organizations; the decolonized world's majority; one-state-one-vote forums), mediatized (press conferences, communiqués, the public stage — and now social media), issue-based (human rights, environment, health — functional regimes beyond high politics), and multi-actor (NGOs, corporations, subnational governments at the table's edges). The continuity to note: the Vienna rules (rank, immunity, protocol) survived — new diplomacy is old diplomacy's shell with a bigger, louder, fairer inside. Nepal's arc in oneline: old diplomacy's latecomer (the Rana-era first missions, the 1923 treaty diplomacy) became new diplomacy's enthusiast (UN, NAM, SAARC, peacekeeping — the multilateral identity Units 4 and 6 detail).