Most, yes. All, no. The biggest westward flowing rivers are the Miño, Duero, Tajo, Guadiana, and Guadalquivir. The largest eastward flowing river is the Ebro.
Small streams flow into rivers and the rivers flow to bigger rivers.
Most rivers begin in the Appalachian mountains or rivers flow into the Gulf of Mexico.
NO
Southeast
Of course there are, the four most important rivers in Spain are the Duero, the Guadalquivir, the Guadiana, and the Tagus.
Actually many rivers run north in North America. Water has no sense of direction. If flows downhill by gravity. Most rivers east of the Rocky Mountains do flow in a southerly direction because the elevation is lower to the south and they are flowing toward the Gulf of Mexico. Source: Riverlorian.com
Mexico
the Mississippi river, Ohio river, and the missouririver are the three most important rivers in the U.S. that flow south.
Gravity, not gods cause rivers to flow. Most rivers in the northern parts of continents flow from south to north.
Most rivers begin in the Appalachian mountains or rivers flow into the Gulf of Mexico.
The Ebro is the river with the most abundant flow in Spain.
Most rivers do not flow to the south. Rivers can only flow from areas of higher elevation to lower elevations, taking the route of least resistence. This is regardless of whether rivers are in the northern or southern hemisphere.