Step 1: Historical context.
The British East India Company gradually established control over India, with major territorial dominance starting after the Battle of Plassey in 1757 (18th century).
Step 2: Establishing rule.
By late 18th century, the Company exercised administrative and military authority across Bengal and later expanded to other regions.
Step 3: Conclude.
\[
\boxed{\text{18th century (Option C) marks the establishment of British rule in India.}}
\]