Complex sentence: In February 1940, the Treaty document was taken to Waitangi for display in the Treaty house during the Centenary celebrations--this was possibly the first time the Treaty document had been on public display since it was signed.
Split into simpler sentences: In February 1940, the Treaty documents were taken to Waitangi for display in the Treaty House during the Centenary celebrations. It was possibly the first time the Treaty document had been on public display since it was signed.