Argentina's Position as a South american country is way more stable than most others, having a small varied supply of Resources, such as steel,oil and tungsten (Which is enough for most of the game) it can Produce military faster in the early game than other South american countries with less need of imports.
At the start of the game, the player should focus on building up the industry as any other country, Military Factories should be a priority, as argentina starts with plenty more civilian factories than military, While the building is on course, The player should also expand the military, However it is worth mentioning that most of the terrain of South america is Hostile, having a lot of ground covered by hills, forest and mountains will make the use of vehicles a challenge, as such, Infantry
divisions backed up by artillery are a good choice to do, Companies that help with terrain such as engineer and Recon companies will be useful. On the same note, An option that will prove useful with the use of artillery would be Overwhelming fire doctrines due to the great ammount of soft attack it gives (Consider that because of the terrain you'll seldom see armor) Although Mass assault and Grand battleplan doctrines also give useful Bonuses Such as Extra manpower and lower Infantry Width Or Extra planning bonus for breaking through the Terrain (again, Most times when attacking you'll have many Maluses)
also recomended that the player starts by going down the Industry Focus tree, as it will provide Civilian, Military factories, infraestructure and near the end of it, and aditional research slot. Which is needed as Argentina only has 2 research slots
Now that when the player has to decide the political leaning, there are some factors that Should be taken into account when Choosing it, Argentina unlike any other country will have a slightly harder time joining the allies, as they have the claim to the Falklands islands and south Georgia, causing a reduction in relations with the United Kingdom. This can easily be fixed with Improving relationships but the political power could be used for anything else.
If the player decides to go facist, They can join the Axis and invade the United States by taking over mexico or through a naval invasion. The same goes for communism just that instead of the axis, the Commitern
In case Argentina cant conquer South america before the Pax Americana focus is complete, a good option would be to Declare war on Portugal to get Resources and a Foothold in europe In case spain has yet to move in. Otherwise the player Should bide their time until they something tips the balance or they amass Enough forces to be comfortable Taking on the US
Once The player Takes over South america they are free to decide how to continue their conquest. it is recomended that by the time They invade the United states (if they go facist/Communist),It is recomended that they possess a great ammount of divisions and have finished the Land doctrines, A Mighty navy is also recomended as the oposing faction will be a Great obstacle in the way of naval invasions.
However if Argentina joins the allies, your main focus should be taking down the remaining enemies. Although betraying the allies later can also be an option, its mostly Up to the player to decide