How can happiness be changed? (Stellaris)

dragont
Build buildings that raise it if available. Rare social technologies.
Wrong domestic policy edicts can diminish happiness.
It depends on the signs of the race itself. Community members have +5 happiness, spiritualists +5 (10). Xenophiles get + to it if they live on a planet with aliens, xenophobes are vice versa.
The governor grants 2% happiness per level.
Can be raised by decrees. There is a technology, after it a decree for +15 happiness opens, but a big minus to production is given.
It also depends on the form of government. Republic of pacifists immediately gives +10.

From buildings - the arena of virtual battles seems to increase happiness + gives a small improvement for armies from the planet

dragont
CiaphasCain
Alien Zoo + 10% gives Teldar Factory + 10% and + 10% for the whole empire.