Byron:
Just in very general terms, the Hungarian First Army had the main responsibility for defending NE Transylvania from 1941 until the spring of 1944. It was the best trained and best equipped Honved army. In the meantime, Hitler demanded the participation of a Hungarian army on the Eastern front, and after much resistance, Horthy consented to sending the newly organized Second Army, with the proviso that Germany would supply most of the needed heavy weapons.
After the collapse of the Don front in January, 1943, the remaining units of the Second Army eventually ended up in Hungarian Erdely (Transylvania), while in the spring of 1944, after the German occupation of Hungary, the First Army was ordered by OKW to Galicia, and was eventually sent on a futile offensive there, losing most of its armor. As the withdrawal continued, the First Army ended up fighting in Slovakia and Poland, but hardly in Hungary.
The main responsibility for defending Erdely fell to the reequipped and reinforced Second Army, alongside German units, when the Soviets and the about-faced Romanians eagerly fell upon the Hungarians. Hope all this helps a little.