No there were not 20 divisions of partisans running around Yugoslavia. 20 real Army divisions in HoI games strategic scale represent something totally different then a ragtag band of partisans. 20 REAL army divisions represent around 30% of the forces the entire United States Army and Marines deployed in WW2 to defeat Japan and do the heavy lifting in liberating western Europe. It represents coordination, radio, hierarchy, trained leadership and men, heavy weapons, vehicle and logistical support among many other things, neither of which the partisans had access to.
OK, I guess someone needs a history lesson. Here it goes.
1. Proleterska Divizija (1st Proletariat division)
By the end of 1944 it had 12.367 men, distributed in 5 brigades including an artillery brigade.
2. Proleterska Divizija (2nd Proletariat Division)
By the end of 1944 it had 9.886 men, by the end of the war it had 10.142 men, distributed in 3 brigades. Also had the artillery brigade.
3. Udarna Divizija (3rd Shock Division)
By the end of 1944 it was engaged in heavy fighting and had only around 5.000 men. From weapons, 330 machineguns (usually German MG), several batteries of artillery, pack artillery and anti-tank guns.
4. Krajiška Divizija (4th Kraina Division)
By October 1944 it had 5.538 men, 65 artillery pieces (light and heavy), 288 machine guns and 8 anti-tank rifles.
5. Krajiška Divizija (5th Kraina DIvision)
Before the arrival of the Red Army and liberation of Belgrade, division had more than 5.000 soldiers and 3 artillery batteries.
6. Lička Divizija (6th Lika DIvision)
By September 1944 it had 5.500 soldiers. It also had an artillery brigade divided into 12 batteries and 2 HQ batteries. This included 6 anti-tank batteries with 24 anti-tank guns (45mm and 76mm), 3 howitzer batteries with 120mm guns and 3 mountain artillery batteries with 75mm guns. 2 HQ batteries were: 1 mixed 76mm/122mm battery, 1 light anti-air battery 25mm.
7. Banijska Divizija (7th Bania Division, later it gained Shock status)
By 1943, after heavy fighting in operations White and Black, the division had 4.100 soldiers, I could not find right now how many where there for the exact division before that.
And I could go on and on.
All divisions (55 by the end of the war) were organized in 16 corps. By July 1944 there were 12 full corps.
After the liberation of Belgrade, it they were all further organized into 4 armies.
By 1942 partisans had 2 airplanes (I know, not visible in the game, but just pointing it out) and by 1944 it had a full air division. 109 officers, 250 NCO and 625 soldiers. It included 110 airplanes, radio detachment, pilot training detachment and mobile repair shop. During the war, partisans made their own bombs for airplanes from piping 100mm and explosive inside, designed by engineer Mile Ljubičić and produced in Ljubija mines in western Bosnia. In March 1944 UK supplied 2 full squadrons of Spitfires and Hurricanes. Partisan airforce ended the war with 3 air divisions. In Soviet Union partisans constructed their own airports i the middle of the marshland.
Officers came from pre-war officer cadre, Spanish civil war veterans, Soviet and domestic officer schools.
It had:
2 Lieutenant Generals (both pre-war colonels of Yugoslav Royal Army)
11 Major Generals (all pre-war officers from rank of captain to colonel)
25 Colonels (most of them Majors and Captains of Royal Army before the war)
67 Lieutenant Colonels
189 Majors
459 Captains
1.124 Lieutenants
880 Second Lieutenants (fresh cadets from partisan schools, 2 years training)
And that was the number of officers in 1943.
Before the arrival of Red Army in October 1944, partisans were supplied with weapons from pre-war depots, Allied drops (included explosives, radio equipment, uniforms, heavy guns and so forth so yes, they had access to all of that) and German depots (captured equipment). Uniforms were either pre-war uniforms of the Royal Army or new ones supplied by the Allies. So it was not some bunch of idiots in rags shooting a few Germans here and there.
It was an organized top-down army, supplied with weapons, ammo, radio (from the beginning several university professors joined and provided aid in radio manufacture, encryption and decryption), medicine (had several filed hospitals). Also, German and Italian light tanks and armored cars. It had its own manufacturing plants for most of the equipment.
In just two months of 1941 (that is the very beginning for you), Partisan weapons factory produced
21.000 rifles
2.700.000 rifle bullets
90.000 pistol ammo
20.000 anti-armor ammo
300 rifle mounted grenades
30.000 hand grenades
300 machine guns
3 artillery pieces
5.000 artillery shells
2.000 land mines
3.000 Molotov cocktails (does not require special equipment, but does require gas and it was in the list so I added it here)
And that my friend is communist resistance. There was also a Royalist one.
By mid 1944 it had 74 brigades, organized into 11 divisions + independent brigades, those further organized into 3 corps. Officers included pre-war Royal army Officers lead by Colonel, later General Mihailović. Other officers included everything from the rank of General to Second Lieutenant of the Royal army. Unlike communist movement, it had no large scale officer school. Additional officers were produced by their service in the field by the decree of pre-war Royal Army General Staff.
The core of the army was specially trained and equipped members of the Stormtrooper battalions made before the war that were tasked to conduct guerrilla war behind the enemy lines. They had specially made equipment, like M24ČK rifles that were issued only to them and had a larger assortment of mobile anti-armor weapons. During the war, they used German, Italian, Yugoslav and UK weapons. UK supplied them regularly up until mid-end 1943 with radios, medicine, weapons, ammo, uniforms. All that equipment was payed by Yugoslav Government in Exile by its gold reserves (nothing is for free). In 1942 alone they got by air drop:
43 artillery pieces
860 shells for them
353 machine guns
3376 rifles and pistols
104 anti-tank rifles
8.728 hand grenades
1.029.450 small arms ammo
2.368kg of explosives
Most of the heavy weapons early on were things hidden during the April War and recovered later. Standard issued on May 27th 1941 was, on 560 man (standard size of Storm battalions, later used as core size for Royal resistance battalions as well): 5-10 mortars, 15-30 machine guns. It meant 60-120 heavy equipment personnel per battalion and the rest were ordinary soldiers. Those battalions formed up brigades, brigades formed divisions and division formed corps.
And here are some pictures of those "rag-tag band of roaming partisans"
Royalist resistance:
Sorry, some were big formats.
And communist resistance:
And some standardized equipment in 1942 and 1944:
And now I dare you to repeat again what you said about rag tag band running around. The communist resistance had by the war end 800.000 troops, Royalist one around 70.000 at its peak in 1943. Yup, just some rag-tag band of bandits and saboteurs I guess.
"That is some scary Partisans that need the attention of 2 out of Germany's 200 divisions." 130.000 soldiers is 2 divisions for you? Sorry, never heard of 65.000 strong division. But that is just me. In mid 1943 Germany had 11 division stationed in Yugoslavia, plus Croatian formations. In total around 300.000 soldiers. By mid 1944 Germany had to field 400.000 troops in order to stop the resistance movements. Compare that to 200.000 soldiers for the Ardennes offensive and you will get the real picture of how scary were those partisans.
You can also find a detailed history of the resistance in Osprey's book "Tito's partisans". It has details about equipment, training of troops and officers, pictures throughout the war and day do day lives of those troops, their logistics system and so on.
Please, do not claim something that you know nothing about.