The river Danube and the South Dobrogea.
This boundary is mainly Danube; and a in the South of Dobrogea a terrestrial border.
This is the boundary with Ukraine: mountains and the river Tisa.
The northern boundary of Bulgaria that separates it from Romania is the Danube River. The Danube River is a very important river that flows through several countries before it reaches the Mediterranean Ocean.
the country that forms the northern boundary of the United States is Canada :)
Carpathian Mountain
This is the river Danube.
The sea that forms the northern boundary of Africa is the Mediterranean Sea. The countries of Morocco, Algeria, Tunisia, Libya and Egypt border it.
red river
The Arctic Ocean
The sea that forms the northern boundary of Africa is the Mediterranean Sea. The countries of Morocco, Algeria, Tunisia, Libya and Egypt border it.
Most of the northern boundary is formed by the Alps. However, on the Iberian Peninsula, the Pyrenees form another northern border of Southern Europe.
soviet union