When it comes to the two opium wars in China's modern history, no one is indignant. Of course, while we strongly condemn the viciousness of the Western aggressors, we are also fiercely attacking the decadence and incompetence of the Qing Dynasty. By the 34s of the 19th century, the Qing Dynasty was already in the grip of corruption among officials, economic development was sluggish, social contradictions were seriously intensified, and it was impossible to recover the predicament of decay that had accumulated for a long time. At this time, Western capitalism was developing extremely rapidly, especially after the Industrial Revolution, and there was already a big gap between the West and China. However, the Western invaders were not satisfied with the status quo, and they began to carry out frenzied colonial expansion in order to open up new markets for goods and raw materials. China has a lot of land and resources, so it will naturally become one of their targets. 
In 1840, the British invaders launched the First Opium War and forcibly forced the Qing Dynasty to sign the Treaty of Nanjing. In 1860, in order to expand their privileges and interests in China, the British and French forces resolutely launched the Second Opium War, invaded the capital, ransacked the Old Summer Palace, and set fire to it, causing many of China's precious cultural relics to be lost overseas or buried in the fire. Of course, there is another country that is the most hateful, that is, Tsarist Russia, which has a credit for sending troops to "mediate" in the war, coercing the Qing to cede more than 1.5 million square kilometers of land, and has become the real winner. However, in this process, we also have a very important question, that is: "Since the British and French forces have invaded Beijing, why did they only burn the Old Summer Palace and not the Forbidden City?"You know, compared to the Old Summer Palace, the Forbidden City is the foundation of the Manchu royal family!"I think there are two reasons for this
First, Britain and France did not want the Qing Dynasty to collapse, as we said above, their move was just to obtain greater privileges and interests in China, so the British and French forces would try to avoid attacking the Forbidden City. Moreover, if the Anglo-French alliance really burned the Forbidden City, it would inevitably force Emperor Xianfeng to the point where he could not surrender, so that Britain and France would not be able to reach peace with China, and of course this could not directly overthrow the Qing Dynasty. Of course, the burning of the Forbidden City will only lead to the expansion of the war between the Qing ** and the Anglo-French coalition forces, so that the Taiping army can profit from it, and will not achieve the original purpose of the British and French **. 
Second, the British and French troops had an agreement with the Qing ** when they entered the city, that is, the Qing army handed over Andingmen to the British and French forces, and promised to "not destroy the city";In addition, it was stipulated that "Coalition soldiers shall not enter the city in large numbers, except for the escort of the ministers of the two countries who will be stationed in the city". At that time, the British and French forces were short of supplies and had to withdraw when the cold winter came, but because of the above agreements, they had to retreat to the second best thing and chose the Old Summer Palace on the outskirts of Beijing as the target of looting. 
Therefore, it is precisely for the above two reasons that the British and French forces did not directly destroy the Forbidden City. But we must not think that without destruction, there would never have been such thoughts. The actual destruction of the Forbidden City is still in the pre-selection plan of the Anglo-French forces. For example, on October 17, 1860, Ergin and Gro both wanted to warn the Qing that if they did not accept our request by the time limit of 20 days, the allied forces would burn the imperial palace in Beijing to the ground." Of course, this warning was not given!On October 18, the British army burned the Old Summer Palace for the second time, and this large royal garden of the Qing Dynasty, "Three Mountains and Five Gardens", was devastated by this group of barbaric and tyrannical invaders, and turned into a ruin. And if after the burning of the Old Summer Palace, the Qing ** still refuses to accept the peace negotiation conditions, the Forbidden City is likely to face such a catastrophe. 