The most common and most likely answer to this crossword clue is the 9 letter word SOCIALISM
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "doctrine" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case doctrine = socialism.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SOCIALISM mean?
SOCIALISM noun- Any of various economic and political theories advocating collective or governmental ownership and administration of the means of production and distribution of goods.
- The intermediate phase of social development between capitalism and communism in Marxist theory in which the state has control of the means of production.
- Any left-wing ideology, government regulations, or policies promoting a welfare state, nationalisation, etc.