The idea for this came from a theory I have, and I'm also not sure how accurate this is with canon. This is the first story I've written in this style.
Many years ago, before there were cards embodied with an easy access to the power of the Tai Chi One Thousand, even before the tablet of the Sky and Earth was split into two separate halves, there was a single tablet; each half twisting to form the yin and yang symbol, the emblem of the Tai Chi One Thousand.
Those of the Sky and Earth lived in peace, except for the occasional fight over who had more control over and could create stronger forms of the characters, such as Fire and Water. After all, they all could equally summon the power of the tablet, and often carried a much smaller version inscribed with their favorite characters.
It wasn't until, that one day, a child that could only use the characters of the Sky was born. No one thought much of it, the child would use get married with one of the Sky and Earth and their child would be normal.
As generations passed more and more children that could only use the characters of the Sky or Earth began to be born, enough for there to be three clans: Sky, Earth, and Sky-Earth. As the clans of the Sky and Earth grew up, they developed a strange ability that caused scales or stripes to appear on their skin, as well as their eyes changing. It gave an immense boost in their skill in using the characters.
Those of the Sky-Earth tried this technique, but most went wild from it, harming many before they were forcibly stopped. Because of how unstable their power was becoming, the clans of the Sky and Earth saw themselves as more powerful, thought their fights always ended very badly with the Sky-Earth clan.
During one of these conflicts, one of the Sky-Earth did was no one thought was possible: summon the power of each of the Tai Chi One Thousand. They had received great power, but at a cost: They mutated into a twisted form of a dragon and a tiger, their mind lost in power. The balance of nature tipped, causing frequently powerful storms that lasted for weeks, abruptly turning into droughts that lasted for months.
It became law then that the clan of the Sky-Earth was no longer to be. It wasn't long before the last of the Sky-Earth clan died.
And so started the constant on and off conflicts of the clans of the Dragonoids and Tigeroids.