Is this sentence a complex sentence:

In 1999 the European Union created a new currency so that it was called the euro.

The sentence doesn't make much sense.

A better complex sentence:

In 1999 the European Union created a new currency that was called the euro.

"In 1999 the European Union created a new currency". This sentence can stand alone. "so that..." is a subordinate clause (dependent clause), and if read by just that portion it wouldn't make much sense. When trying to figure out if a sentence is complex simply split it into two sentences and read it out loud. It also is helpful to look at a list of subordinate conjunctions

Ms. Sue is right. As it stands, the sentence makes no sense. It is, however, a complex sentence in a grammatical sense. Rune is right, too, but his explanation would confound me. Study this for a clear understanding of simple, compound, and complex sentences:

http://www2.ivcc.edu/rambo/eng1001/sentences.htm

Yes, the sentence "In 1999 the European Union created a new currency so that it was called the euro" is a complex sentence.

To determine if a sentence is complex, we need to check if it contains an independent clause and one or more dependent clauses.

In this sentence, "In 1999 the European Union created a new currency" is the independent clause because it can stand alone as a complete sentence.

The dependent clause "so that it was called the euro" adds extra information and cannot stand alone as a complete sentence. It relies on the independent clause to make sense.

Therefore, since the sentence contains both an independent and a dependent clause, it is classified as a complex sentence.