America should steer clear of foreign alliances when it has liberty to do so
<em>Baruch S. Blumberg invented </em><span><em>a vaccine for smallpox for which he won noble prize in 1976.</em></span>
Answer:the the threat of disease
Explanation:
<span> Well here answer my the Crop rotation system began developing in Britain towards the time of the agricultural revolution which increase crop yields by increasing the nutrients in the soil. </span>
