However, this can easily be done by mid-1941 or so. Reacquiring and keeping your core provinces should be your minimal goal. The Romanian provinces can be annexed peacefully via The Second Vienna Award, that lowers your relationship with Romania in return for more land.

Yugoslavia can be invaded early on, or you can wait for Germany and/or Italy to help. Aligning with the Axis early on grants the Czechoslovakian portion of territory to be gifted to Hungary, and also provides a route to attack Poland and gain even more territory. In some way, shape, or form, you'll be wanting all of these territories.

These include parts of Czechoslovakia, Yugoslavia, and Romania. One of the interesting things about Hungary are its core provinces in other nations. Otherwise, it's possible to try to go at it alone, conquering neighbors before the war goes fully underway and becoming a true world power. They provide an excuse to invade and annex neighbors, are easy to join before the war begins, and are a major power in your part of the world. Of the three factions, Hungary is best aligned with the Axis, as in real life. Make sure to build new air bases as necessary there aren't many in this area. Last off, be sure to have at least a small air force of Interceptors for defensive purposes. Ignore naval power having a coast is a best-case scenario for Hungary, and there's no way any navy you'll make will match that of the British or Italians. You can also support them with Artillery brigades to give them the extra firepower they need. Combined with its large starting army of infantry, it is therefore advised to make an infantry-based army, with appropriate technologies. Hungary has enough IC to build armor and the like, but is lacking the resources to make the most of them. Plus, there will be chronic resource shortages, made even worse by the lack of any coastal provinces. Unfortunately, it's lacking in Leadership and Technology, and the divisions are generally undersized. It also starts with a fair number of infantry divisions and plenty of generals. Hungary is a regional power, with less Industrial Capacity and Manpower than the great powers like Germany and the Soviet Union, but still a fair amount.

Hearts of iron 3 manpower