NEW DELHI (AP) — When the British ended two centuries of colonial rule on the Indian subcontinent in August 1947, they left a jigsaw legacy — the vast country of India flanked on either side by a newly created Pakistan split in two parts. Excitement over independence was quickly overshadowed by some of the worst bloodletting the world has ever seen, leaving up to 1 million people dead as gangs of Hindus and Muslims slaughtered each other.

As the 70th anniversary of India-Pakistan Partition comes up next week, relations between the two nations are as broken as ever. In some ways, their violent birth pangs dictated their future course through suspicion and animosity.

Here's a look at the troubled legacy of Partition:

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FAMILIES DIVIDED

Muslim refugees take shelter in Purana Qila, the old fort, Sept. 17, 1947. (AP Photo/Max Desfor)

India's independence leaders had proposed a secular federation where Hindus and Muslims would live together. The Muslim League, representing the region's 30 percent Muslim minority, said it wanted a separate nation to be free of perceived oppression by the Hindu majority.

Creating two independent nations, however, tore apart millions of Hindu and Muslim families in one of the world's largest peacetime migrations. Many fled their homes and lost their property, never imagining that they would not be able to return. At least 15 million people were displaced.

As relations between India and Pakistan soured, travel restrictions and hostile bureaucracies kept many from crossing the border to visit family and friends. The countries make a few exceptions for religious pilgrimages, allowing small groups of Hindus, Muslims and Sikhs to visit holy sites during religious festivals. Recently, New Delhi has allowed ailing Pakistanis to come to India for medical treatment.

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NUCLEAR BRINKMANSHIP

A Brahmos missile at a Republic Day parade rehearsal, 2009. (AP Photo/Gurinder Osan)

India and Pakistan have fought three wars and built up their armies but also developed nuclear weapons.

India was the first to conduct a nuclear test in 1974. The test elicited an angry reaction from Pakistan, where Prime Minister Zulfiqar Ali Bhutto said his countrymen would be prepared to eat grass if they had to go nuclear.

India didn't conduct nuclear tests again until 1998. Pakistan followed with its own nuclear tests just a few weeks later. Experts say the two sides have since armed themselves with hundreds of nuclear warheads as well as missile delivery systems.

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THE KASHMIR QUESTION

Indian soldiers search Kashmiri Muslims in Srinagar in 2002. (AP Photo/Rafiq Maqbool)

No issue has bedeviled India-Pakistan relations like the disputed Himalayan region of Kashmir.

Soon after gaining independence, both sides claimed the majority-Muslim region in its entirety. Kashmir's Hindu ruler wanted to stay independent, but local uprisings and a raid by Pakistani tribesmen drove the maharaja to seek assistance from Indian troops.

This spiraled into a yearlong war that ended with a U.N.-brokered ceasefire and Kashmir divided between the two young nations by the heavily militarized Line of Control.

Kashmiri discontent with Indian rule took root as successive governments reneged on a promise to allow a referendum. India and Pakistan fought a second war over Kashmir in 1965 that resulted in little change.

When a full-blown rebellion erupted in 1989, India deployed even more troops to the region. Thousands of Kashmiri fighters staged bloody attacks on Indian security forces and on pro-India Kashmiri politicians.

In the last decade, the rebellion has been suppressed and most anti-India sentiment is expressed in regular street protests by tens of thousands of civilians. They are sometimes quelled by deadly force.

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GLACIER BATTLEGROUND

Indian army camp at Siachen Glacier, northwest of Jammu, India, in 2005. (AP Photo/Channi Anand)

The Line of Control ends abruptly at Siachen Glacier, a 6,100-meter-high (20,000-foot-high) icy Himalayan expanse that is the world's highest battlefield.

Thousands of troops have been deployed on the glacier since 1984, laying claim to territory so hostile to human life it has never been demarcated. Far more troops have died from avalanches or bitter cold than in combat.

While there are no clear borders on the glacier, its position between the Indian and Pakistani-controlled portions of Kashmir makes it a key part of any final map that may be drawn of the region. Its high altitude gives its occupants an advantage over those below.

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ELUSIVE PEACE

Pakistani Prime Minister Nawaz Sharif, Indian Prime Minister Atal Bihari Vajpayee at the Wagah border, Pakistan, Feb. 20, 1999. (AP Photo/B.K. Bangash)

The many efforts to resolve their longstanding disputes have all, so far, been in vain.

In 1999, Indian Prime Minister Atal Bihari Vajpayee revived peace talks and took a groundbreaking bus ride to the Pakistani border town of Lahore to meet his Pakistani counterpart, Nawaz Sharif.

But less than four months later, Sharif's army chief, Gen. Pervez Musharraf, sent armed invaders into Kashmir to capture some mountain peaks. The move provoked two months of air strikes and ground attacks by India, ending after Sharif ordered the fighters to withdraw. Musharraf would go on to topple Sharif in a coup.

Negotiations were put on hold for years after five attackers infiltrated India's Parliament and killed nine people in 2001. Relations were further strained in 2008 when Pakistani gunmen killed 166 on a rampage across Mumbai.

In 2014, Indian Prime Minister Narendra Modi began his term on a conciliatory note by inviting his Pakistani counterpart, again Nawaz Sharif, to his oath-taking ceremony.

The next year, Modi paid a surprise visit to Sharif's home in Lahore. But the friendliness dissolved days later when gunmen, allegedly from Pakistan, killed seven soldiers at an Indian air force base. Months later, Modi ordered a surgical strike on alleged insurgents inside Pakistani-controlled Kashmir, and vowed to isolate Islamabad diplomatically.

India accuses Pakistan of sponsoring terrorism, a charge Pakistan denies. Peace talks are unlikely to resume any time soon.

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CHINA TO THE NORTH

The rise of China as an economic powerhouse has further strained India-Pakistan relations. Beijing has long supported Islamabad, creating additional strategic and military concerns for New Delhi. China offered financial and technological help to Pakistan in developing its nuclear and missile programs. Now it is developing a major highway and port in Pakistan as part of an effort to link China with the Middle East and Europe.

Global alignments have tested India-Pakistan ties before. During the Cold War, a U.S. tilt toward Pakistan led India to turn to the Soviet Union for support, military hardware and defense technology.

Today, India maintains strong ties with both the United States and Russia, making it unlikely that any potential conflict with Pakistan would stay between the South Asian neighbors.

"Indian strategy under Narendra Modi should be to ensure that major external powers such as Russia and the United States continue to remain in its corner to ward off the possibility of a two-front war by China and Pakistan against India," said Sreeram Chaulia, professor at the Jindal School of International Affairs.