The blitzkrieg, which is German for "lightning war," was an effective German strategy in World War II because it took full advantage of the new ideas of mechanized warfare with bombers, fighter planes and tanks to soften up the enemy and create terror before sending in infantry troops. This caught many countries off guard because they were accustomed to the more traditional tactics used in World War I.
Dive bombers, specifically the Stuka, would rapidly approach a target and unload their munitions. In the chaos of the explosions, Panzer tanks would roll through the enemy's defensive line and fire at targets of importance. Finally, the infantry soldiers would come in to pick off stragglers.
Germany used mechanized forces in a way that had not yet occurred to other countries, some of whom were still thinking in terms of static battle lines as used in World War I, or in the case of England, had not yet realized the importance of air power. Mechanized warfare allows the offense of a combatant to maneuver more quickly through terrain and bring the heaviest force to bear from the outset of an assault as opposed to sending fighting personnel into a fresh battlefield. The blitzkrieg's overall effectiveness only lasted for a few months to a year because the Allies caught onto Germany's tactics and adapted.