Holding the Scottish referendum settled the independence question and ended the risk of the union being eroded "bit by bit", David Cameron said.
In his main conference address, the Prime Minister highlighted the role of Scottish Conservative leader Ruth Davidson in winning the campaign.
And he told activists in Manchester the final week had been "the most nerve-wracking" of his life.
Mr Cameron said: "I am so proud to stand here today as Prime Minister of four nations in one United Kingdom.
"I was always clear about why we called that referendum. Duck the fight, and our union could have been taken apart bit by bit. Take it on, and we had the chance to settle the question.
"This party has always confronted the big issues for the sake of our country. And now England, Scotland, Wales, Northern Ireland, we are one people in one union and everyone here can be proud of that."
He also pledged that increased devolution for Scotland would be matched with "English votes for English laws" at Westminster, promising: "The Conservatives will deliver it."
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