Complex sentence: The size of a budget also reflects the entity's ability to fund military activities, with factors including the size of that entity's economy, other financial demands on that entity, and the willingness of that entity's government or people to fund such military activity.
Split into simpler sentences: The size of a budget also reflects the entity's ability to fund military activities. Factors include the size of that entity's economy, other financial demands on that entity, and the willingness of that entity's government or people to fund such military activity.