AVA- Gavin Williamson told Tory activists the wars had restricted public appetite to join conflicts overseas.
A total of 456 British troops died in Afghanistan from the start of 2001, and 179 in Iraq from 2003.
Speaking on the Tory conference fringe in Birmingham, he launched a passionate defence of intervention.
He told the Conservative Home/Raytheon event: “Our confidence was knocked by the conflicts in Iraq and Afghanistan, in terms of actually we became too timid in terms of saying, 'Do we get involved?'
“But where Britain's strength has always been, our great strength has always been as a nation to have the confidence and have the belief to say that we are doing this because it's the right thing to do, it's in our national interest to do.”
Recent months have seen a gradual increase in the number of UK troops based in Afghanistan.
“This is us rediscovering the fact that intervention - when it is thought-through, when it is properly considered - is the right thing to do and Britain is an important part in terms of making that happen,” he said.
Mr Williamson also rejected criticism of comments he made earlier this year in the wake of the Salisbury Novichok attack on a former Russian double agent Sergei Skripal , 67, and his daughter Yulia, 34.
The nerve agent assault was blamed on the Kremlin, and the Scarborough-born Defence Secretary said Russia should “go away and shut up”.
He told Tory supporters: “One of my either great virtues or great faults is that I am blunt.
“I am afraid I ain't gonna change, that's just what's in the DNA of every Yorkshireman.”