I started a Dai Viet campaign just for fun, not really intending to do anything grand.
In a successfull attempt to reenact a war yet to come, I first swiftly annexed my southern neighbour. I thought being of different religions would give me a CB, turns out we were in the same group. I declared war anyway. We gained control over Vijaya and Panduranga, uniting all of modern Vietnam under our banner.
At that point I started a very uneventful series of royal marriages with everybody. If "harassment" could be judged by international laws, khmer would probably have filed a case against me. It seems though that it was all vain, as our nation was more frequently guided by a regency than an actual monarch. Lucky for us, kings in the whole region suffered from the same exceptionally poor life expectancy and fertility. I did also behave very aggressively, claiming thrones left and right, which most of my neighbours didn't like at all.
After a while, we somehow obtained claims on a Siem Reap, owned by khmer. It is still mysterious to me why exactly we received this as that province was only adjacent to one of the provinces we just had taken from Champa (south vietnam), and had of course no legitimity to hold it. Anyway, our monarch jumped on the occasion and we won a very clean war, taking the province with us.
The events that follow were quite messy but I'm pretty sure they involve freeing a 1-province Ayutthaya in Rayong from the korean dominion (yes, Korea had the great idea to take land over there) and quickly turning them into vassals. And also retaking Prey Konor lost by those lazy Khmer to the Malaccans, in the name of religious protection.
The state of the country in 1480 :
I surprisingly managed to maintain decent relations with China. But Pegu, which is way too powerful, hates me, along with everybody I know except Tibet (yay !), Manchu (yay !) and Ayatthaya (which are my vassals anyway). That would be fine if said Pegu didn't had a core on Rayong, which means I'm very regularly at war with them.
I got rich provinces and only one is uncored, but I had to use mercs in my first war against Pegu and my inflation is off the charts.
All in all, I made a lot of bad decisions early on and I don't think I'll be playing this save again xD