Technology Tree
The technology tree is different for each faction but has a basic format that is the same for each side. Tech levels 1 - 3 are linear and so the player has no choice but to advance one after the other. However past tech 3 the tree opens out. The various branches allow the player to choose were to focus their research. If the strategic situation is going badly on the ground then they may with to focus on better tanks while losses in the air may demand immediate advances in aircraft. By using the tech tree to gain a temporary edge in one area of the battlefield a shrewd player can time their economic spending to coincide with tech advances and thus maximise the effectiveness of their forces.
Experience Points
There are three sources of income in Blitzkrieg. The first is the command centre. Your command centre represents the high command of your nation and as such recieves an income based on the availible military budget. This income can be boosted during the course of the war. The Axis and Soviets can shift their economy to a total war setting, greatly boosting the income their command centre generates. Soviet players should also request Lend-Lease shipments as soon as possible because these will deliver both payment in kind (military equipment) and hard currency. The Allies do not get a total war bonus, but when the US intervenes in the war the huge American economy will greatly boost the Allies income, allowing them to afford the expensive high-grade equipment favoured by their military leaders.
Buildings
The Blitzkrieg technology tree is used to represent the passage of time. Skirmish games start in 1939 and the player will have the standing army and technology available to their nation in 1939 at the outbreak of war.
Right away they will begin receiving technology points. These build up slowly over time but will also be recived (like in Generals) for fighting in battles. In reality many advances in World War II were from lessons learned from the battlefield, or even directly copied from captured enemy vehicles.
One thing is for certain - to keep the technological edge it is vial to fight in battles. Even if you loose you will gain points that can boost your technology and give you an edge the next time you fight. Be wary of simply throwing away your troops though. You may give your opponent a decisive edge in the race for better technology. One minute of game time represents roughly one month, and so to progress from late 1939 technology to mid 1945 technology will take roughly an hour of gameplay. This will vary greatly on how much one fights, and a very good general may be fielding Maus tanks and jet fighters well inside of this time.