A 15-year-old girl arrested for waving a banner; hundreds bundled into police vans; journalists targeted with water cannon.

More alarming than these sights in Hong Kong, yesterday, was a police message: "You are displaying flags or banners chanting slogans or conducting yourselves with an intent, such as secession or subversion, which may constitute offences under the HKSAR national security law."

The law, which had just come into force, gives the police power to arrest anyone whose behaviour they deem subversive. It has caused an international outcry, with Britain's foreign minister, Dominic Raab, describing it as a "clear and serious violation" of the treaty China and the UK signed in 1984.

He added that three million Hong Kong citizens will be given the right to move to Britain.

Meanwhile, in a sign of growing concern about China's strategic ambitions, Australia's prime minister, Scott Morrison, has announced $270 billion (150bn) in defence measures, including long-range missiles and hypersonicTravelling at speeds of more than five times the speed of sound (Mach 5). weapons.

Are the politicians overreacting?

Muscle-flexing Chinese armed forces have been behaving aggressively on several different fronts, sending aircraft carriers on manoeuvres off TaiwanAn island country in east Asia. China still claims to be the legitimate owner of Taiwan, while the Taiwanese government until recently claimed to be the legitimate government of the whole of China., chasing Japanese fishing boats in the East China Sea and killing 20 Indian soldiers in a border clash. China has also used its economic power to secure mineral resources in Africa; buy everything from property to vineyards in Europe, and create a new trade route for itself through its belt-and-road initiative.

Limitless resources China has the world's largest population - around 1.4 billion people. It has the largest standing army (2.3 million troops) and is Asia's strongest naval power. Its economy will overtake the US and become the world's largest in about 2030 - and it is already the world's biggest trading nation and manufacturer.

Deeply different values China has far less respect for individual freedom than Western democracies. Its repression of the Uighur people is on an extraordinary scale: over one million of them have been detained in camps for "re-education", and women are being forced to undergo sterilisation.

Natural dominance China is the third-largest country in the world by land mass (after Russia and Canada), with an enormous population - now comprising 18% of the global total, and rivalled only by India. For most of history, it has been the world's dominant power. It is only natural that it should reassert itself.

Epic civilisation China is one of the world's oldest civilisations, responsible for the "Four Great Inventions": the compass, gunpowder, paper, and printing. Under its auspices, the Silk RoadA network of Eurasian trade routes linking China to the West, running from the second century BC to the 15th Century AD. was arguably the most important trade route in history. China has given us Confucian philosophy, exquisite porcelain, painting and poetry, and outstanding food.

Happiness Though Westerners tend to see the Chinese as repressed, millions of them are perfectly happy. One expert, the former chairman of HSBC, Stephen Green, points to their "vibrant, modern mindset", their patriotism and "a growing sense of self-confidence, civic pride, and engagement".

Yes. The new law in Hong Kong is the shape of things to come. "This is the last nail in the coffin," says the dissident Chinese artist Ai Weiwei. He argues that the China's totalitarian government has no interest in engaging with democracy, and the main aim of its latest move is to send a signal to Taiwan that its days of independence are numbered.

No. It is natural for China to seek stability at home and pursue its interests abroad. Stephen Green argues that we should engage with Beijing, not shun it: we may have grown used to a world dominated by America and Russia, but that is not the historical norm. We should open our eyes to China's cultural riches and welcome what it has to offer.

Secession: The act of withdrawing from something. Some of the Hong Kong protesters would like the territory to be completely independent of China.

Subversion: The attempt to weaken or destroy a political system or a government.

Deem: To consider or judge.

Hypersonic: Far faster than the missiles now in use, hypersonic ones are designed to travel at five times the speed of sound.

Taiwan: After communist forces won control of China in 1949, their nationalist opponents retreated to the island of Taiwan and set up an independent state. The Chinese have offered Taiwan a similar status to Hong Kong if they are allowed to take over, but most Taiwanese oppose the idea.

Border clash: Because Chinese and Indian troops have an agreement not to use firearms on the border, they resorted to using sticks, stones, and their bare hands.

Vineyards: Chinese investors have bought around 175 vineyards in Bordeaux since 2010.

Belt-and-road: Launched in 2013, this scheme now embraces nearly 70 countries that give China access to their sea, road, and rail links in return for investment in their infrastructure.

Naval: To do with ships.

Uighur: An ethnic minority distrusted by the Chinese government because their Islamic faith gives them a system of values different from communism.

Sterilisation: An operation to permanently prevent pregnancy.

Under its auspices: With the help and support of.

Silk Road: A 4,000-mile route which connected China to the Mediterranean. Merchants took silk westwards along it, and wool and precious metals eastwards.

Confucian: Confucius ( around 551-479BC) was a philosopher who emphasised the importance of justice, kindness, and education.

Hypersonic - Travelling at speeds of more than five times the speed of sound (Mach 5).

Taiwan - An island country in east Asia. China still claims to be the legitimate owner of Taiwan, while the Taiwanese government until recently claimed to be the legitimate government of the whole of China.

Silk Road - A network of Eurasian trade routes linking China to the West, running from the second century BC to the 15th Century AD.