As we all know, in the 289 years of the Tang Dynasty, the capital Chang'an was always the official capital of the Tang Dynasty, and if the Tang Dynasty Emperor lined the Luoyang Palace as an excuse to say that the Tang Dynasty moved the capital to Luoyang, it is really absurd. According to the view of the Luoyang people, then the Qing Dynasty Chengde was not also the capital, because the Qing Emperor often traveled back and forth between Beijing and Chengde, and often handled the imperial government at the Chengde Palace, received foreign envoys, and many officials even built private houses in the Chengde enclosure, it can be said that the status of The Qing Dynasty Chengde was no less than that of Luoyang in the Tang Dynasty.
A large reason why Wu Zetian moved to Luoyang was that Chang'an, as a capital of the country, had become too large to provide for. As a capital, it is inevitable that a large number of people will be gathered. Business as a eunuch, a pawn of a peddler, a royal family, and a huge and complex population made Chang'an look like a bloated fat man. They need a lot of supplies. This is something that Chang'an itself is difficult to satisfy. Although there is also land to cultivate here, it is more dependent on food transferred from outside to meet consumption.
In addition to agricultural technology, in order to increase agricultural production, only to reclaim more land to cultivate, and the Guanzhong area is actually a narrow basin, the north is the Loess Plateau, the reclamation of land will inevitably have to cut down forests, coupled with the real estate development brought about by the rapid population of Chang'an, so that the demand for timber continues to rise, naturally making the ecological environment in Guanzhong more deteriorating.
There can be more than one companion in all dynasties, but there is only one official capital of the French system, as can the Western Zhou and Sui and Tang dynasties. To misinterpret by any means the two capitals system, the two capitals, as one dynasty with two capitals at the same time, is a gross distortion of history.