Hundreds of thousands of Vietnamese fled their country after the Communist victory over the US-backed forces of South Vietnam in 1975.
Now, as the BBC's Nga Pham has been finding out, the Hanoi government is trying to lure some of the diaspora back to the country to help it modernise.
Overseas Vietnamese are welcomed by the government
With red flags and loud revolutionary music, the gathering inside the massive National Conference Hall in Hanoi's outskirts resembles a regular meeting of Vietnamese political cadres, only with better-cut suits and more fluent English.
This is the first meeting of Vietnam's diaspora to be held inside the country, attracting nearly 1,000 Vietnamese living overseas for a three-day conference.
It is being hailed by Vietnam's official media as a "major step towards national unity" for a nation that was ravaged and divided by decades of war.
Vive la difference?
Bui Kien Thanh, 77, a senior financial adviser, has spent half his life living in France and the United States.
"I first went overseas in 1949 to study, but then came back to work for [former South Vietnamese President] Ngo Dinh Diem," he says.
"After Mr Diem was toppled in a coup, and the war continued, I left Vietnam again in 1965."
After working for American insurance giant AIG, Mr Thanh was invited back by the Vietnamese Foreign Ministry in 1991. Since then has acted as an economic and financial adviser to the government.
"Some people criticised me as naive and pro-communism when I returned to Vietnam, but I knew what I was doing," he says.
"I believe in democracy, in market economy and the state of law and that's how I want to help change this country."
"See how fast Vietnam has been changing. We can do something different for our nation," Mr Thanh adds.
Time for change
Another delegate, Nguyen Ngoc My, is equally excited about the changes in Vietnam.
Mr My served in South Vietnam's navy during the war. After the North Vietnamese took over in 1975 he was put in a re-education camp for more than two years until he fled to Australia by boat in 1978.
"I used to take part in anti-Hanoi protests whenever Vietnamese government officials visited Australia, up until 1986-1987, when Vietnam began the reform process."
In 1992, Mr My started making made regular visits back and since 2000 he has spent most of his time in Vietnam pursuing a number of investment projects. He eventually become chairman of the Overseas Vietnamese (or Viet kieu) Business Club in Ho Chi Minh City.
But he admits that there are still parts of the Vietnamese diaspora who remain suspicious of the country's Communist rulers.
"Some of them would never come back to visit, let alone to invest or do business here."
Is talk enough?
The purpose of the Viet kieu meeting, according to chief organiser Nguyen Thanh Son, who is also vice minister of foreign affairs, is to provide them with a forum to discuss issues close to their hearts.
Mr Bui Kien Thanh feels there is space for change in his home country
"A large number of the Viet kieu left Vietnam in despair and hatred when the war finished," he says.
"This is an opportunity for them to see and to understand what has been happening inside the country."
It took the Hanoi government years and a budget of 8bn dong ($450,000; £270,000) to organise the conference.
But there is criticism that the conference has "missed the point", as all the delegates are seen as pro-regime and cannot represent the whole diaspora.
Tran Nam Binh, an Australian Vietnamese who teaches at the New South Wales University, decided not to go to the conference and doubts that it can bring about any "concrete results".
"I don't think this kind of meeting will make any tangible change, even in the government's policies towards the Viet kieu. So I don't regret not taking part."
Money and brains
There are nearly four million Vietnamese living overseas, mostly in the United States.
Each year, they send relatives back home up to $10bn, a major source of hard currency in the communist country.
But knowledge and expertise, not money, are what the government expects most from the Viet kieu.
Many returning Vietnamese had a chance to meet and greet each other
Vietnamese experts living overseas are being urged to come back to teach and contribute their skills to the country.
In 2004, the Vietnamese government began a series of legal changes to give the Viet kieu rights to re-claim their Vietnamese citizenship and even to own property in Vietnam.
But for some, economic incentives are not enough for them to consider coming back to Vietnam.
Dr Hoang Kim Phuc, a scientist at the University of Oxford, England, sees a lack of respect from Vietnamese officials for the country's intelligentsia.
He thinks that only when local experts are treated properly, can the government hope to receive support from Vietnamese living overseas.