Broken concrete block
To "stabilize" this house, someone wedged a broken piece of concrete under the support beam.
Cracked wood
Most houses are supported by a beefy main girder, this house is not. It looks like someone tried to level the floor with a wedged in brick.
Inadequate support
These beams are not supported well at all, they are uneven and could easily fall apart.
Bad support
With no footers, these support piers can sink and settle into the ground over time. This causes even and sagging floors.
Exterior wall
With many older homes, the traditional foundation walls we are used to just don't exist. They are supported by stacks of whatever material was available.
Concrete blocks
In an area where the floor is sagging, many people just add a few concrete blocks under the wooden supports. When these begin to settle, the floor sags again.
Crushed wood
The wood warps and crushes from the weight of the home and the high moisture in the wood.