It began as an autonomous constitutional monarchy with the Russian empire with its own legal system,
It began as an autonomous constitutional monarchy with the Russian empire with its own legal system, parliament, and army.  Nicholas I paid scant attention to its liberal constitution, however, and the Organic Statute of 1832 effected a true union with Russia.  Nationalist sentiments led to the January Insurrection of 1863 in Warsaw, but the Russians soon crushed it, effectively ending any autonomy this state may have had.  FTP name this kingdom set up as a Russian puppet state at Vienna in 1815.
It began as an autonomous constitutional monarchy with the Russian empire with its own legal system, parliament, and army.  
Congress Kingdom of Poland