The accurate statement about nation states is:
D. In the modern world most countries are nation states.
Explanation: A. This is incorrect because not all countries are nation states; some are multi-national or have diverse ethnic groups without a dominant nation. B. This is incorrect as a country can be a nation state without having two official languages; the definition does not require a specific number of languages. C. This is incorrect because the first nation states emerged much earlier, particularly in the 17th and 18th centuries, well before the 20th century. D. This is correct because most countries today are organized as nation states, where a political entity corresponds closely with a specific national identity.