China is expected to buckle down on reunifying Taiwan after the mainland almost completely excluded pro-democracy and anti-Communist activists from the political arena in Hong Kong by overhauling the territory's electoral system.

If China tries to conquer Taiwan by force, it could also become hostile toward Japan as the close U.S. ally is likely to work in tandem with Washington to support the democratic island, complicating the security and diplomatic situation in East Asia.

Despite mounting criticism from many democratic countries, the leadership of President Xi Jinping has accelerated measures to tighten its control over Hong Kong, as the ruling Communist Party marks the 100th anniversary of its founding.

As Xi has pledged to attain "the great rejuvenation of the Chinese nation," his next ambitious goal would be the reunification of Taiwan, which has been separately governed from the mainland since they split in 1949 as the result of a civil war, observers say.

On Thursday, Hong Kong's legislature approved a sweeping electoral overhaul ordered by China to ensure that only Beijing loyalists rule the city. China's parliament in March passed a resolution on altering the electoral system in the territory.

China's move has triggered a backlash from democratic countries and escalated already existing tensions with the administration of U.S. President Joe Biden, which has criticized Beijing's alleged human rights abuses since it was launched in January.

Xi's leadership, however, has taken strict actions against the special administrative region since large-scale protests sparked by a now-withdrawn extradition bill with mainland China morphed into a pro-democracy movement in 2019.

In late June 2020, Beijing enacted a controversial national security law for Hong Kong to crack down on what it regards as secession, subversion, terrorism and collusion with foreign forces.

In the mainland, many Chinese citizens have apparently provided positive support for Xi's hard-line policy against Hong Kong.

"Chinese, who have persevered under Communist rule, have basically disliked Hong Kong people, who have benefited from freedom and democracy for the past decades," a diplomatic source said.

Under China's "one country, two systems" policy, the former British colony was promised it would enjoy the rights and freedoms of a semiautonomous region for 50 years following its return to Chinese rule in 1997.

Around 20 years ago, Hong Kong's economy accounted for one-fourth of China's gross domestic product as the city developed as an international financial hub, but the scale is now only about 3 percent, analysts say.

"Hong Kong people have been adequately blessed with democracy and freedom and recently received economic benefits from China, although they have always acted like victims of the mainland," a 39-year-old Chinese woman told Kyodo News.

As for Taiwan, most Chinese citizens believe that the self-ruled island should be reunified with the mainland in the future, given that it has been dependent on the world's second-biggest economy, the diplomatic source said.

"Many of them think peaceful reunification should be achieved on the back of China's overwhelming economic power, but some argue that the Communist Party should use military might," he said.

Beijing has endeavored to undermine the island's quest for international recognition, while its repeated incursions into Taiwan's air defense identification zone and naval exercises in nearby waters have fanned concern about a possible Chinese invasion.

For years, meanwhile, China has extended an olive branch to its neighbor Japan, the world's third-largest economy, as its relations with the United States have shown few signs of improving soon.

But China has been irritated by Japan since Prime Minister Yoshihide Suga confirmed with Biden at their summit in Washington in April "the importance of peace and stability across the Taiwan Strait."

It marked the first time in 52 years that Japanese and U.S. leaders have mentioned Taiwan in a joint statement.

Immediately after the summit, the Chinese Foreign Ministry summoned a senior official of the Japanese Embassy in Beijing to lodge a protest against the agreement between Washington and Tokyo.

"China has begun to adopt a tougher attitude toward Japan," the diplomatic source said. "To put pressure on Tokyo, it may send more coast guard ships to the waters near the Senkaku Islands and conduct military drills in the East China Sea more often."

Beijing claims that the uninhabited islets administered by Tokyo in the East China Sea are part of its territory, calling them Diaoyu in the country.

In February, China enforced a bill allowing its coast guard to use weapons when foreign vessels involved in illegal activities in waters it claims do not obey orders, raising fears that Japanese ships navigating around the Senkakus would be targeted.

Moreover, if China and Taiwan are engaged in military conflict, the United States would send its forces to defend the island from its bases in Japan, which would prompt Beijing to take more provocative actions once it sees Tokyo as an "enemy" of the Communist Party.

"We do not know whether China will use forces in a bid to reunify Taiwan, but the Japanese government has to seriously consider how to deal with such a contingency," the source said.

Since the administration of former President Donald Trump, the United States has been stepping up its support to Taiwan amid deepening rifts between the United States and China on issues including trade, technology and Hong Kong's autonomy.

In 1979, when Washington switched its diplomatic recognition from Taipei to Beijing, the U.S. Congress passed the Taiwan Relations Act.

Under the act, the United States maintains substantive though unofficial relations with Taiwan and supplies the island with arms and spare parts to enable it to secure sufficient self-defense capabilities.