Conversation so far:
How were the Sinhalese kingdoms formed?
Tambapanni.
Who or what are the Tambapanni?
landed on the island at a site believed to be in the district of Chilaw, near modern-day Mannar, and founded the Kingdom of Tambapanni.
Is this were the Sinhalese live today?
after the death of Vijaya and the end of the Kingdom of Tambapanni.
Who is Vijaya?
Prince Vijaya and his 700 followers left Supparaka, landed on the island at a site.
Did he take over the Sinhalese people?
Tambapanni was originally inhabited and governed by Yakkhas, having their capital at Sirisavatthu.

Question: Were the Sinhalese people always there?
Self-contained rewrite: Were the Sinhalese people always at Tambapanni?