How would having a high blood pressure lead to cardiovascular disease?

Several mechanisms: - damages blood vessels by harming cells lining them. - causes increased work/strain for heart muscle, causing it to enlarge (like any muscle that gets worked) ; over time, this process may result in impaired relaxation of heart (so it can't fill with blood) and dilation and weakening. High BP may cause hard/stiffening/narrowing of blood vessels (and thus not enough flow) also.

Trauma.: There are many theories to how elevated blood pressure leads to cvd. The most accepted theory is that of trauma and stress. Think of a fast running "high pressure" river... The banks of the river will feel more stress and accumulate more damage and irregularities over time than a slow creek. This same damage occurs to the vascular intima (or lining of our blood vessels) when exposed to high bp.