noun
people of all nations; world's people
A somewhat formal or literary term referring to all the people of the world collectively. Not an everyday word; often found in older or idealistic contexts.
万国民の平和を願う。
I wish for peace for the people of all nations.
人類 is the common word for 'humanity' or 'mankind'. 万国民 is more specific to the people of various nations and has a slightly old-fashioned or formal tone.
Compound of 万国 (ばんこく, 'all nations') and 民 (みん, 'people'). The exact historical derivation is uncertain, but it follows a common pattern of Sino-Japanese compounds.