41 years ago on the morning of May 15th, I watched a parade.
Hundreds of victorious North Vietnamese troops and tanks along with carefully choreographed young "National Liberation Front" supporters streamed down the street in front of Saigon's Presidential Palace. Russian and Chinese made vehicles carried the soldiers. A colleague joked: "Vietnamese soldiers fight awfully well but just can't march."
Over the previous sixteen days, I had witnessed -- the last Americans leave the U.S. Embassy, T-54 tanks sweep into the city, the first of millions of refugees flee toward the South China Sea, and a new Communist-led government consolidate power across all of Vietnam.
[Video: May 15 1975]
On May 14th, the top North Vietnamese leaders arrived in Saigon for the first time. With them from Hanoi came a small diplomatic corps including the Ambassadors from the Soviet Union and the People's Republic of China.
There was this day a display of solidarity; solidarity between Hanoi leaders and those of the National Liberation Front or Provisional Revolutionary Government of the South -- the forces we used to call the "Viet Cong." A display of solidarity too among the Vietnamese and their Russian and Chinese allies.
Without their Chinese and Russian allies, Hanoi could not have won the war.
Reports from the C-I-A, declassified between 2001 and 2008, chronicle "endemic competition" between Moscow and Beijing in supplying weapons to North Vietnam between 1965 and 1973.
The Russians provided the bulk of Hanoi's air defenses while the Chinese provided "a range of weapons and routine ground level assistance," sending in ground troops to assist in logistical and construction support.
All of this cooperation was soon to fall apart. The May 15th rally was an illusion in many ways.
Vietnam's relations with China grew steadily worse. Vietnam invaded Cambodia and grew closer to the Soviet Union. China seethed.
Four years after the American war, the Vietnamese were using Chinese weapons to defend themselves against the invading donor.
In late March 1979, I stood amid rubble in Lạng Sơn Vietnam only 12 miles south of China's Guangxi Province.
Chinese and Vietnamese forces had just ended a 29 day border war there. China's had launched an incursion to "teach Vietnam a lesson."
In its aftermath, northern Vietnam was again on a war footing. Ethnic Chinese residents joined the flood of refugees fleeing Vietnam. Anti-Chinese sentiment grew to alarming levels.
[Video: April 1, 1979]
Sixteen months ago, I was back in Vietnam once more, speeding along the spectacular central coastal region north of Da Nang. My companion -- a very talkative taxi driver.
Like China, Vietnam has changed beyond recognition in the nearly 40 years I have been visiting these communist neighbors. Nearly every year since 1979, I have returned to one or the other or both to witness astounded economic progress.
But some things don't change.
My driver in Da Nang asked me where I was going after I worked my way up the Vietnamese coast.
"From Hue to Hanoi and then on the Beijing," I replied.
"Oh, China," the driver declared in clear but halting English, "you know, we Vietnamese hate the Chinese. We've hated them for a thousand years."
It is actually more than two thousand. The Vietnamese speak of four periods of Chinese domination; the first from about the year 100 BC.
Monuments in various parts of the country celebrate the Trưng Sisters -- Hai Bà Trưng -- the two remarkable women warriors who fought the Chinese and died bravely in combat in the year 43AD.
In most Vietnam towns and cities there is a "Lê Lợi Street;" in honor of the Vietnamese Emperor-hero who beat the Chinese, ending Ming Dynasty domination in 1427.
Professor Qiang Zhai, a Chinese historian who has charted the course of the two nations from Imperial times to when Mao Zedong met Ho Chi Minh in 1959 to forge an alliance, says the two are locked in a centuries old "love-hate relationship."
This week, President Barack Obama enters the fray with a visit to Vietnam. He is the third U.S. President to travel there since the war. (I traveled with the first -- Bill Clinton -- in November 2000.)
Obama goes to Vietnam as Hanoi-Beijing tensions are again on the rise.
Last November, efforts by President Xi Jinping to ease those strains by addressing Vietnam's parliament appear to have fallen on deaf ears.
The two socialist neighbors and comrades in revolution and war should be able to survive "disruptions" and go on to be "win-win partners" said Xi. He received a cool reception and little applause. Xi's failure to mention the long simmering South China Sea territorial dispute except obliquely prompted MP Duong Trung Quoc to remark: "Mr. Xi can speak of China's interests, but Vietnam's interests cannot be pushed aside."
In January, Vietnam protested a Chinese move to place an oil rig in alleged Vietnamese waters. In 2014, a similar move by China sparked major riots in Vietnam.
Two months ago, Hanoi police did nothing to stop anti-Chinese demonstrations.
The territorial dispute centers around what Western nations in the 19th Century named the Spratly and Paracel chains -- islands stretching hundreds of miles south of the large Chinese island of Hainan.
Vietnam says its active rule of these areas began in the 17th Century and that China did not lay claim to them until the 1940's. China disputes that. [The Philippines also lays claims to some of these islands]
At stake are an estimated 11 billion barrels of oil in the region, additional quantities of natural gas, and trillions of dollars in trade passing through the sea lanes.
In the past, the Hanoi leadership seemed split on how to handle Beijing. What Americans might call 'hawks' and 'doves" sit on Vietnam's ruling politiburo. Today Hanoi seeks counterweights to what they see as continuing Chinese provocations.
Hanoi's Ambassador to Washington, Pham Quang Vinh, has called for the complete lifting of America's embargo on weapons sales to Vietnam.
President Obama will likely not go that far. Half measures have already been implemented.
In October 2014, Washington approved the sale of U.S. made patrol boats to bolster Vietnam's coast guard.
The U.S. will likely move forward and OK military requests on a case-by-case basis.
The Vietnamese also have other options. The Russians have been open to arms sales to Hanoi at lower prices for years.
Much recent focus has been on Vietnam's key naval port of Cam Ranh Bay. The port on the central coast has been described as the finest deep water port in Southeast Asia.
A major U.S. base during the American War, Cam Ranh was leased to the Soviet Union in late 1979. Russia pulled out in 2002. Since then the port has been modernized and has received visits by warships from Singapore, Japan and France.
The U.S. Navy has enjoyed increasing cooperation with Vietnam's Navy since 2004. That year, the port of Da Nang (320 miles north of Cam Ranh) received the first U.S. warship since the war. Look for what the Pentagon calls "NEA:" Naval Engagement Activity to be expanded.
Further advances in United States-Vietnam relations will likely emerge in the next few weeks. What also seems clear is that as US-Vietnam ties grow, preventing conflict between two of Asia's oldest adversaries -- Vietnam and China -- will be a major diplomatic challenge in the years ahead.