Why would the number of consumers in a market shift the demand curve left or right?

In an effort to end the civil war, in 1864 the union planned to

It can be inferred that the dramatic increase in defense spending by germany was the result of. (a) attempts by great britain to take german colonies. ( b) fear of a two-front war against france and russia (c) the need to put down a communist rebellion (d) a competition with the allies to produce atomic weapons

Who did the first work in creating vaccines