Baseball's system of organizing professional teams is quite complicated but be split into two categories

Organized

Independent

Independent Baseball

Teams and leagues in independent baseball are not under the authority of the Commissioner of Baseball and do not have relations with MLB or MiLB. Currently includes eight different leagues across the country. 

Organized Baseball

Teams and leagues in organized baseball are under the authority of the Commissioner of Baseball.  Currently this includes Major League Baseball and Minor League Baseball.

The MLB is the highest level of baseball in the world. For baseball players, the goal is to reach this level

For the bottom three tiers, the teams play shortened schedules. Teams in Short Season A have a 76 game schedule, while the Rookie teams play schedules of 56-76 games, with the exact number depending on the team.

The Mexican League is the only league in organized baseball where its teams are not affiliated with a major league team.

When a player is drafted, where the player is sent depends on the skill and development of the player. For example, 2017 No. 1 overall pick Royce Lewis was drafted out of high school and sent to Rookie Ball while No. 3 overall pick Branden McKay was selected out of Louisville was sent to Short Season A ball.

The Atlantic League is the consensus top independent league in the country. The league has eight teams mostly in the Northeast and Mid-Atlantic area.

These four leagues are very at the bottom of the totem pole of professional baseball in North America. For many of the players in these leagues, this is their only shot to every play pro ball.

The American Association is in the second tier of independent baseball and has probably rose above the Can-Am League in terms of play over the last few years. The Chicago Dogs play in the American Association

The Frontier League has been around since the 1990s. ​The Leagues has three teams in the outer suburbs of Chicago.