Croatia had been armed by Germany before 1990...

In addition, there was a weapons embargo imposed as soon as Croatia declared independence, which required Croatia to smuggle weapons in, and froze the balance of power where the Serb paramilitaries had JNA backing and Croatia effectively had no army. It took 3 years (and a side war in Bosnia to keep the JNA busy) for the balance to be reversed.

Most economists teach a theoretical framework that has been shown to be fundamentally useless. -- James K. Galbraith