Now is no exception.
In recent weeks, China and Vietnam have been jockeying for position in the contested patch of ocean.
This isn't the first time they have done so — back in 1988 some 70 Vietnamese died in a brief naval battle between the two powers — but it is the first time tensions have significantly boiled over in nearly a decade.
Both China and Vietnam are more powerful now and both have increasing energy needs as their economies grow.
The sea is thought to be oil- and gas-rich, which is a main reason — in addition to it being home to important shipping lanes — why it continues to be a source of contention. Sovereignty has long been contested and it remains an emotive issue for Chinese and Vietnamese populations.
The Philippines, Taiwan, Brunei and Malaysia also claim parts of the Spratly-Paracel archipelago located in the sea, which is known in Vietnam as Hoang Sa and Trung Sa.
Most recent spat
On Monday, Vietnam conducted what they called "routine" live-fire drills off the coast, following accusations that China interfered with PetroVietnam's ships in the sea. Beijing prickled, saying Vietnam's actions constituted a "show of force to defy Beijing."
That same day, Vietnam's Prime Minister Nguyen Tan Dung signed an order clarifying who is eligibile for military conscription, which will be effective from August. It wasn't a call to order, but it was a military directive at a time of heightened tensions.
While experts say there isn't likely to be out-and-out war this time around, most say more clashes are almost certainly on the horizon.
Last week, Dung called Vietnamese sovereignty in the area “incontestable,” while "Beijing has adopted the attitude of a wearily vexed but patient patron," said Gavin Greenwood, an analyst at the Hong Kong-based security firm Allan and Associates.
"[China has long signalled that its] claim to the South China Sea is … non-negotiable,” Greenwood added.
Vietnam authorities permit protests
For a couple weeks now, uncharacteristic protests have erupted outside the Chinese embassy in Hanoi, and its consulate in Ho Chi Minh City.
Public displays of dissent are rare in Vietnam. When they do happen, they generally concern issues that directly affect everyday life, like land grabs or factory conditions.
Police reportedly outnumbered protesters at these recent marches, but the fact that authorities allowed them to occur at all is notable. Previously, they have cracked down — perhaps most notably in 2007.
“Clearly, the authorities had the capability of ensuring the anti-China demonstration did not even begin, but chose to permit it — either to allow public opinion to be ‘vented’ or as a signal to Beijing that the dispute had crossed an important line,” said Greenwood.
China and Vietnam have a contentious history. Northern Vietnam was occupied by the Chinese for more than 1,000 years, and anti-Chinese sentiment can run high there. Outwardly, however, the two nations mostly make a show of friendship.
Nguyen Thi Hoa, a 60-year-old Hanoi resident, said she has been following the latest spat closely.
“I don’t understand why China wants to do this,” she said, speaking from Hoan Kiem Lake in Hanoi's city center, a few hours after the protests on Sunday morning.
“This is our land, our house, our nation. China cannot invade. It’s very clear. But the Chinese cannot accept they are wrong!”
How likely are future clashes?
Experts don't think another war is imminent, but many in Vietnam would not like to see their government back down either. Future clashes may be inevitable.
Vietnam expert Carl Thayer, a professor in Canberra, told GlobalPost that "both China and Vietnam are heading for a collision course if they do not stop upping the ante in response to each other.”
The sentiment was echoed by Greenwood, who said, “A minor incident between the two countries naval or coastguard units that ended the present period of mounting tension may be inevitable as neither side can readily back away from their present positions.”
Last year in July the United States said that that resolving the ongoing issue was in the United States' “national interest.”
Foreign ministry spokeswoman Nguyen Phuong Nga said that Vietnam welcomes international efforts in the sea dispute.
"Every effort by the international community in maintaining peace and stability in the East Sea is welcome,” she wrote on her official website.
Many have taken Nga’s comments as a call for United States assistance, but at least one expert says that won't happen anytime soon.
“The U.S. has a national interest to see that U.S.-owned ships and those of its allies and friends and ships that carry cargo to and from the United States are not molested," Thayer said. "But the U.S. will not take sides in territorial disputes."