The Greeks, Persians , Japanese, Chinese, Slavic, Brittons, Welsh... just to name a few all have dragons in there mythology, is there a root dragon that they all took inspiration off? How on earth could the Chinese and Greeks both have a version of dragon without ever contacting each other? Dragon existence confirmed?
Recently, I answered this question about dinosaur fossils and dragons; it addresses the core of your question.
If we break your question apart, we can dismiss many of the international supposed-examples of dragons: just because English-language speakers use the same term for foreign monsters does not mean that all the monsters are the same and/or related. The same thing occurs with terms like 'fairies' and 'elves' which are often applied to the international spectrum of supernatural beings. The similar use of an English word does not imply any profound similarities or relationship. People internationally conceive of monsters and human-like supernatural beings, but this only describes the situation in the most generic of terms. Differences are more profound than similarities and no connection can be taken to be implied.
On the other hand, some concept of the dragon may be related through historical and prehistorical diffusion. This is more difficult to pin down, but it seems that as Indo-European languages spread, certain aspects of a core pantheon and belief systems spread as well. This included a large monster, often associated with water that the culture hero was compelled to slay. That can be taken to be an explanation for at least some European and perhaps Persian expressions of monsters that English-speakers identify with the term 'dragon.'
About a year ago, I answered a similar question here which may help expand on u/itsallfolklore 's answer.