At its peak, the Tang Dynasty, especially during the reign of Emperor Gaozong of Tang, covered an area of 12.37 million square kilometers after conquering Goguryeo and Baekje. During the Qianlong Dynasty, the heyday of the Qing Dynasty, the area reached 13.16 million square kilometers. It can be seen that although the territory of the Tang Dynasty is smaller than that of the Qing Dynasty, it is not much smaller, that is, hundreds of thousands of square kilometers.
We may wish to compare the territory of the Tang Dynasty and the Qing Dynasty.
west
According to historical records, the western part of the Tang Dynasty reached the Aral Sea and Afghanistan. For a long time, the Qing Dynasty faced pressure from the Dzungars, and it was not until the Qianlong period that the Dzungar Khanate was eliminated, and its power continued to extend, but only to the Pamir Plateau from Lake Balkhash.
Therefore, from the perspective of the western border, Datang far exceeded the Qing Dynasty.
south
The southern part of Datang reached the territory of Annam. During the Qianlong period, the territory reached the Nansha Islands, but it did not include Annam, which was only a vassal state at that time.
north
Emperor Gaozong of Tang pushed the northern border to the north shore of Lake Baikal after the Great Destruction of the Western Turks; the northernmost part of the Qing Dynasty reached Kyakhta (south of Lake Baikal and north of the Sejang River).
east
Generally speaking, we often say that the east is to the sea, but in fact, it is still different. During the Tang Dynasty, after the pacification of Goguryeo and Baekje, it occupied most of the Korean Peninsula and established the jurisdiction of the Andong Protectorate.
And this point, obviously, the Qing Dynasty is incomparable, the Qing Dynasty and Korea have a clear boundary is along the Tumen River, Yalu River boundary.
northeast
In the northeast, the Manchu Qing dynasty was definitely more territorial than the Tang Dynasty. During the Manchu Qing Dynasty, the northeast stretched to waixing'anling, Sakhalin Island, and the Sea of Okhotsk. The gap during the Tang Dynasty was very large, and Emperor Gaozong of Tang did not fully occupy the vast area of northeast China.
southwest
The gap between the two sides in the southwest is a bit large, and Tubo in the Tang Dynasty is not included. In the Qing Dynasty, it was different, and The Qinghai-Tibet was already in the territory of the Great Qing.
Therefore, in summary, the peak period of Datang had farther radiation in the border area, but many places did not exist for a long time. The Qing Dynasty was more direct than the Northeast and the Qinghai-Tibet region, and its control over Mongolia was relatively more direct than that of the Tang Dynasty.