In The Phenomenology of Spirit, "spirit" or "Geist," can mean spirit or mind, but its German definition is quite broad and can include notions such as culture and human mental activity in a wide range of disciplines throughout history. And, this refers to each individual mind/spirit as one unified, collective Mind/Spirit. For Hegel, the study of history is a way to understand this collective Mind/Spirit and how it interacts with and influences history.
Hegel suggested that the history of Mind/Spirit had been the history of Mind coming to know itself. Hegel's theory of historical development is based upon a dialectic, which is illustrated in three phases of thesis, antithesis, and synthesis. In the development of Mind, Hegel begins with being (thesis), nonbeing (antithesis), and the synthesis of these opposites is becoming. This becoming is, with respect to Mind/Spirit, the coming to know itself as the ultimate reality. This dialectic, or synthesis, shows the abstract and material function of change when opposing and/or conflicting ideas exist together. This dialectic or triadic development is called Entwicklung.
Hegel also uses the "Master/slave dialectic" (Lordship and Bondage) to illustrate the dialectic of Consciousness, Self-consciousness and Absolute unity. Hegel writes this development abstractly enough that it can refer to an individual or all of human history. The idea is that, via some relationship, such as master/slave, a self-consciousness can only attain this Absolute unity if it recognizes and is recognized by another self-consciousness. The master (thesis) enslaves the slave (antithesis). Over time, the master comes to depend upon the slave and thus, the slave has enslaved the master. The master becomes its other (slave). Now, a synthesis is possible in which the outcome will be that each recognizes each other as an equal. Each self-consciousness, via conflicts of ideas and historical relations, recognizes other self-consciousnesses, resulting in a recognition of the collective consciousness: Mind/Spirit, the Absolute.
Hegel uses the term "aufheben" to describe these syntheses of consciousness and history. Aufheben means to negate but also to preserve. The antithesis negates the thesis, but the synthesis preserves something of each. This is shown in the reciprocated relationship with the synthesis of the master/slave when the relationship is reversed and finally, when each sees the other as an equal, a reciprocating connection.
Terms of the dialectic:
In itself (an sich)
For itself (fur sich)
In and for itself (an und fur sich) - This is the synthesis, the Absolute reality where consciousness merges with its own being. The individual (consciousness) becomes free when he/she becomes aware of these dialectics, i.e., to recognize other ideas, other events, and other people, not as something external to ourselves but as parts of the collective Mind/Spirit.
Although quite complex, Hegel's thought is, simply put, based upon individual, historical, and Ideal syntheses.
A ↔ B → C.