The most common and most likely answer to this crossword clue is the 8 letter word MAINLAND
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More clues leading to the result MAINLAND
Buddy explains!

The straight part
We know that "country’s bulk" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case country’s bulk = mainland.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 MAINLAND mean?
MAINLAND noun- The continent; the principal land, as distinguished from islands or a peninsula.
- The principal island of a group.