AKTAU, Kazakhstan -- Russian President Vladimir Putin and the leaders of four other countries surrounding the Caspian Sea came together in mid-August to divvy up the world's largest inland body of water and its potentially enormous oil and natural gas reserves.

They met in Aktau, a strategic Kazakh port town, and signed a deal to settle a two-decade-long dispute over those resources. Their motivation for finally burying the hatchet, most likely, was the battle for regional hegemony between Russia, China and the U.S.

The venue was fitting, since Kazakhstan is right in the middle of the fray.

Russia, Kazakhstan, Iran, Azerbaijan and Turkmenistan agreed, in principle, to accept territorial waters stretching 24 km from their shores, plus fishing areas extending out another 16 km. The rest of the sea is to be shared.

The governments also agreed to build underwater pipelines and cables across the Caspian, unless environmental concerns preclude the projects.

Kazakh President Nursultan Nazarbayev hailed the signing of the Aktau Convention at the Caspian Summit on Aug. 12 as a "historic event."

When the nations of Central Asia emerged after the collapse of the Soviet Union, they had high hopes for tapping the Caspian's resources for export to Europe. "Today in Aktau, in front of the entire world, we can say that we have managed to reach a common denominator and understanding as a result of joint work," said Nazarbayev, who has been president since the office was established in 1990.

The deal, though, is only part of a much bigger game. China is expanding its regional clout through the Belt and Road Initiative, which includes the development of a trade route through Kazakhstan and the Caspian Sea to Europe. The U.S. and Russia, meanwhile, are wrestling for control of key Kazakh ports.

Many observers say Moscow was the driving force of the Aktau Convention.

The agreement "ensures the Caspian Sea's truly peaceful status and the absence of extra-regional states' militaries there," Putin said after the summit.

That last part -- the military factor -- seems to have been the Kremlin's primary concern. Russia, which sees the Caspian as part of its sphere of influence, is alarmed by warming U.S. relations with Central Asia.

The leaders of countries surrounding the Caspian Sea mark their agreement on territorial waters in Aktau, a Kazakh port town, on Aug. 12.   © AP

Nazarbayev's visit to the White House in January set the tone.

Kazakhstan amended a 2010 agreement with the U.S. on using commercial railways to move special cargo for the stabilization and reconstruction of Afghanistan. The deal was expanded to add the ports of Aktau and nearby Kuryk to the Northern Distribution Network -- a catchall for supply routes supporting the war effort.

"I greatly appreciate the president's personal assurances that Kazakhstan will continue to provide critical logistical support and access for our troops fighting ISIS and the Taliban, where we have made tremendous strides," U.S. President Donald Trump told a media briefing after his summit with Nazarbayev.

The U.S. is also using its annual "C5 Plus 1" consultations with five countries of Central Asia to enhance its involvement in the area. While this is geared toward Afghanistan, it is a useful mechanism for pressuring Russia as the bilateral relationship sours.

Zhumabek Sarabekov, a foreign policy expert with the state-run Institute of World Economics and Politics in Astana, explained Kazakhstan's mindset when it comes to strengthening ties with Washington.

"We have our own national interests and we are interested in developing and expanding a strategic partnership with America," he said. "Given the geographical factor and, as a result, insignificant bilateral trade, cooperation in the security sphere is a key for Kazakhstan, especially when America is present in Afghanistan and is carrying out the operation there."

U.S. President Donald Trump, right, hosts Kazakh President Nursultan Nazarbayev at the White House in January.   © Getty Images

When the Kazakh ports were officially included in the U.S. distribution network this past spring, Russia did not take the news well.

The media and public figures slammed Astana, claiming it had offered its ports to the U.S. for military bases. Kazakh officials have repeatedly denied this, arguing the deal is similar to what Russia has done in the past.

"Naturally, there is no talk whatsoever about any military bases on the Caspian Sea," Kazakh Foreign Minister Kairat Abdrakhmanov stressed in an interview with Russia's RIA Novosti news agency.

Still, the Aktau Convention gives a leery Russia a buffer against the growing American presence. Putin's next goal is likely to be expanding Russia's own military footprint in and around the Caspian.

"I would like to inform that the strategy of the development of seaports in the Caspian basin by 2030 has been adopted and is being implemented in Russia," Putin told the summit in Aktau. Noting the prospects for a "comprehensive upgrade of Caspian Sea routes, related rail and road infrastructure," he said that a "new deep-water port of Kaspiysk is to be built by 2025."

As Moscow and Washington continue their tug of war, Beijing is pulling Kazakhstan in a third direction.

On Aug. 11, the eve of the Caspian Summit, Nazarbayev attended the opening of a multimodal transport hub at the port of Kuryk. "This is important not just for our country but for all of Eurasia, especially for our brotherly neighboring countries," he said. "And, if you think of it, it connects the Pacific Ocean with the Persian Gulf, Black Sea and Mediterranean Sea across the Caspian Sea."

Nazarbayev made a point of saying the country's transport projects are "part of China's Belt and Road Initiative."

The president said Kazakhstan had been working hard to establish transcontinental transport links between Europe and Asia, and had modernized the port of Aktau and built the port of Kuryk to accommodate 26 million tons of combined cargo capacity a year. This, he suggested, was in anticipation of surging flows of goods between China and Europe over land, which cuts the travel time to 13 to 14 days as opposed to 45 by sea.

Nazarbayev, center, attends the opening of the port of Kuryk on Aug. 11.   © Getty Images

Nazarbayev further boasted that these ports have direct railway and road links to the Khorgos dry port on the Kazakh-Chinese border, which, in turn, is linked to the Chinese port of Lianyungang on the Yellow Sea. Kazakhstan has also built thousands of kilometers of railways and motorways to improve connectivity.

Nazarbayev suggested Kazakhstan's transport networks would earn the country about $9 billion a year by 2020.

It is clear that Kazakhstan is a critical part of the Belt and Road vision. Chinese President Xi Jinping first announced the initiative there in 2013 -- a fact Xi brought up in June when he welcomed Nazarbayev in Beijing and lauded the progress made over the last five years.

Experts see factors that could hinder China's ambitions in the region. "The Caspian route is very expensive," said Nargis Kassenova, director of the Central Asian Studies Center at Almaty's KIMEP University. "That's the main impediment to its development."

Even so, the route offers Beijing some alluring benefits. Development requires cooperation with just three countries -- Kazakhstan, Azerbaijan and Georgia. Unlike other major Belt and Road routes connecting Asia with Europe, the Caspian route does not pass through Russia. This helps China contain the long-term political risks of its grand vision.

From Kazakhstan's perspective, Belt and Road involvement offers a chance to wean itself off Russia by bridging China and Europe.

A freight train is pictured in Changsha, China, before departing for Tehran. The Belt and Road Initiative hinges on railway links through Central Asia.   © AP

For now, China and Russia are putting on a show of solidarity as tensions with the U.S. mount. The Chinese armed forces are expected to participate in Russia's biggest military drills to date, set to start on Sept. 11 in the Russian Far East and Siberia.

Beijing and Moscow appear to be getting along over the Caspian, too, at the moment. But if China draws Kazakhstan deeper into its orbit with the Belt and Road, it could lead to more friction with Russia.

In the early 20th century, British geographer Halford John Mackinder argued that the country in control of the "heartland" of Eurasia, mainly Central Asia, had the potential to rule the region and the world. With the global order now in flux, the struggle for the heartland is heating up again.

Kazakhstan has much to gain but also faces a difficult balancing act, as it seeks constructive ties with a trio of major powers pursuing conflicting interests.

"Kazakhstan has now become a subject of global geopolitics," Sarabekov, the Kazakh foreign policy analyst, said. "Our role is not to passively watch what's going on around us, but we ourselves can also regulate this process."

Sarabekov emphasized that his country's position is "that we want to make friends with everyone." Yet he also conceded that this diplomatic approach is "becoming increasingly difficult and is even becoming a luxury."

Tomoyo Ogawa in Moscow contributed to this article.