What is the "Great Firewall" and how does it work? The digital barrier that China uses to control internet access.

Over the past three decades, China has erected a digital barrier separating the global internet from a filtered and controlled version for its citizens.

This system, known in the West as the Great Firewall , is one of the most sophisticated tools of censorship and information control in the world. And it doesn't just define how more than a billion Chinese users browse the Internet: these days, that wall has also become a central player in trade tensions with the United States .

A firewall A firewall is a security system that acts as a barrier between a private network and the rest of the Internet, filtering incoming and outgoing traffic according to defined rules to block unauthorized access and allow secure access. It can be software, hardware, or a combination of both, and works by inspecting circulating data to decide whether to allow it through or block it. Firewalls began to be used in the late 1980s, when the growth of networks and the first computer threats made the need to protect connected systems evident.

Initially conceived in the mid-1990s, the Great Firewall is the visible face of a larger project known as the Golden Shield Project. Under the direction of the Chinese Ministry of Public Security, and later the Cyberspace Administration of China, this mechanism is tasked with blocking entire websites, filtering content, and ensuring that what circulates in the country is "compatible" with the interests of the Communist Party. In the words of the authorities, its objective is to "safeguard the public interest."

Unlike the open internet that dominates much of the world, what happens within China's borders is more like a " splinternet ": a fragmented version where authorities decide what can be seen and what can't. Social networks like Facebook, Instagram, and Twitter, search engines like Google, international media outlets like Reuters and The New York Times, and services like Dropbox, Netflix, and YouTube are all off-limits to Chinese users, replaced by local alternatives like WeChat, Weibo, and Bilibili.

The tension between this wall and the attempts to tear it down has not stopped since its creation. While authorities improve their blocking techniques, users explore ways to circumvent it through VPNs, proxies, or the Tor network. However, the current context of the trade war with the United States has once again tested the flexibility and political intent of this digital giant.

The Great Firewall works by combining several inspection and blocking techniques. All information entering and leaving China through land-based access points is inspected, allowing authorities to identify and shut down entire domains or IP address ranges. This constitutes the first line of defense , complemented by more sophisticated mechanisms to detect banned keywords or phrases in searches and traffic.

When a user attempts to access a blocked term or site, the system can intervene in several ways. One is Domain Name System (DNS) manipulation, in which addresses are rerouted or "poisoned" to prevent the page from loading. It can also directly block IP addresses or even reset network connections through "reset" attacks on the TCP protocol. In some cases, it intercepts encrypted data using man-in-the-middle attacks to inspect packets that should be private.

But the monitoring doesn't end there. Authorities also actively track evasion attempts, detecting connections to proxy servers, virtual private networks (VPNs) , or Tor nodes. While these methods still allow, with some effort, to breach the wall, advances in surveillance have reduced their effectiveness and increased the risks for those attempting to circumvent the restrictions.

In addition to blocked foreign services, the Chinese digital ecosystem has robust local alternatives. In the absence of Google, users rely on the Chinese version of Bing. Instead of Uber, they have Didi. Social media centers on WeChat and Weibo, while platforms like Bilibili and iQiyi dominate video streaming. In this way, the wall not only limits external information but also creates a captive market for local tech giants.

However, this strategy comes at a price. Censorship limits the diversity of opinions and can reinforce more nationalist views, as well as fostering the spread of state-controlled disinformation. In 2011, when the US questioned restrictions affecting American companies, Beijing defended the wall, arguing that it sought to " maintain a healthy internet environment and safeguard the public interest ," claiming that such measures were in line with international practices.

That 2011 episode set a precedent. Then-Foreign Ministry spokesperson Jiang Yu emphasized that China would not accept the principle of "internet freedom" as an excuse to interfere in its internal affairs. At the same time, she asserted that foreign companies were still welcome to do business in the country , albeit under the rules of China's digital environment.

Today, the Great Firewall is once again at the center of the dispute between China and the United States , this time as a tool to control domestic discourse in the face of escalating tariffs. In April of this year, following the implementation of US tariffs that reached up to 104% on Chinese products , authorities began censoring related content on social media.

On Weibo, searches and hashtags linked to "tariff" or "104" appeared blocked, displaying error messages. At the same time, posts ridiculing the US proliferated, such as a hashtag launched by state television about an alleged egg shortage in the United States, used to downplay the impact of the measures. This manipulation of the flow of information reflects how the wall not only protects the population from foreign messages but also helps shape the official narrative during economic conflicts.

The pattern was repeated on WeChat, where multiple posts from Chinese companies warning about the negative consequences of US tariffs were deleted. The deleted messages were labeled as violating laws and regulations, reinforcing the idea that any content perceived as harmful to the state must disappear.

The censorship didn't just suppress domestic criticism: it allowed, and even encouraged, mocking comments about the US, portraying it as an irresponsible and aggressive trading partner. Thus, while China implemented its own tariffs in response, the domestic narrative reinforced the narrative that Beijing had no choice but to "fight to the bitter end."

Local experts and commentators also contributed to this discursive construction. Lawyer Pang Jiulin asserted that other countries, such as Vietnam and India, would soon replace China in exports to the US, and that the tariff increase would be a necessary sacrifice. Renowned analyst Hu Xijin, for his part, called the US strategy "illusory" and predicted that its "war against the world" would fail.

In this context, the Great Firewall not only filters sensitive information , but also becomes a key instrument for maintaining domestic morale and preparing public opinion for the economic consequences of the trade war.

While the Great Firewall has always been a national policy, recent research shows that it is deepening at the regional level, creating inequalities even within China. A study published this year revealed that users in Henan province were deprived of access to five times more sites than the national average between November 2023 and March 2025.

The analysis, conducted by the Great Firewall Report platform in conjunction with researchers from the University of Massachusetts Amherst and Stanford, found that Henan blocked nearly 4.2 million domains, compared to the 741,500 that the centralized system typically censors. This appears to be related to financial protests in the province and the government's fear that information about the economy could escape its control.

While it's unclear whether the additional restrictions in Henan were imposed by local authorities or Beijing, they set a worrying precedent: the possibility of entire regions being subjected to harsher censorship than the national average. This is reminiscent of what happened in Xinjiang and Tibet, where controls were always stricter because these were considered conflict zones.

The techniques have also become more sophisticated. Artificial intelligence-based tools allow for monitoring VPN use and even spying on messages sent via Telegram, an app considered key by those trying to evade censorship. According to the Ministry of Public Security, these tools have already collected more than 30 billion messages , raising surveillance to unprecedented levels.

This combination of increased regional censorship, technological control, and internal fragmentation suggests that the future of the Chinese internet will be even more restrictive and unequal. If the wall was once a national border, it now appears to be multiplying into smaller walls within the country itself, tailored to the political and social needs of each region.

The Great Firewall was born as a tool to control the narrative and protect social stability. But recent research shows that this mission has become more ambitious and expansive. Beyond tensions with the US, the digital wall also reflects China's own internal tensions, and its need to control not only what enters the country, but also what circulates within it.