Morale.
Morale is lost in several ways.
Pop limit is reached (-1 per turn, unless at planet physical maximum)
combat above planet (not sureof minus number here)
losing a colony (-5)
A colony of the same race is destroyed (-5)
Losing your flagship dreadnought loses morale
Morale losses can be reduced with the presence of a police cutter. These are destroyer sized ships, just one will reduce morale loss. For example one police cutter in orbit stops the -1 morale loss through hitting pop limit. A police cutter is available after you research trade and fusion.
Morale loss doesnt occur from population limit if you allow the whole planet to be filed up, at which point you lose resources for being above the sustainable planet population.
Morale loss from population is also halted by building a colony ship that turn.
Morale is gained from.
1 million in savings will net +1 morale a turn
5 million in savings nets +5 I think
10 million nets more (cant remember I never have that much saved up as I spend it too fast)
A new colony grants more moral.
Maximum number of trade routes running gives + 1 morale.
Propaganda ships (cruiser class vessels) will grant +5 morale whilst in orbit. Unless your liir.
I may have missed a few.
Higher morale can mean higher productivity.
Early game how do I stop my morale loss on planets?
Simplest solutions.
Solution 1: Move the pop slider to the max and damn the resource loss. On non production worlds it doesnt matter and it will be a good 100 to 200 turns before you really mess the planet up.
For those a little less destructive.
Solution 2: Save 1 million. Simple to do, and easy, just stop researching for perhaps 3 turns, and stop spending money until you have 1 million. Just make sure you keep 1 million in the bank each turn to counter morale loss through pop limit.
Solution3: feeling rich? build a new colony ship every turn at the worlds with the pop problem. Benefit is that you can drop a lot of colony ship at the next suitable world.
When you get trade.
Solution 4:
build enough freighters for 1 per trade route and use all trade routes. Although you maximise the trade benefit by having 5 freighters per route.
When you get fusion
Solution 5:
Build police cutters at all worlds.
1 and 2 are the best solutions early game.