one Primary Key Value in many tables : This may seem like a simple question, but I am stumped:

I have created a database about cars (in Oracle SQL developer). I have amongst other tables a table called: *Manufacturer* and a table called *Parentcompany*.
Since some manufacturers are owned by bigger corporations, I will also show them in my database. 
The *parentcompany* table is the "parent table" and the *Manufacturer* table the "child table". 
for both I have created columns, each having their own Primary Key. 

For some reason, when I inserted the values for my columns, I was able to use the same value for the primary key of *Manufacturer* and *Parentcompany*

The column: **ManufacturerID** is primary Key of *Manufacturer*. The value for this is: 'MBE'

The column: **ParentcompanyID** is primary key of *Parentcompany*. The value for this is 'MBE'

Both have the same value. Do I have a problem with the thinking logic? 
Or do I just not understand how primary keys work?
Does a primary key only need to be unique in a table, and not the database?

I would appreciate it if someone shed light on the situation.

Donovan