Answer
Coal spontaneously combusted
Explanation
There are many theories for the cause of the United States the USS Maine  explosion with Us men aboard where many died. According to the United States  Naval  Investigative team team their research concerning this incident , they came to a conclusion that the explosion was caused by fire that had ignited the ammunition stock.  According to these investigators there was a strong  evidence that the explosion of Maine was caused by an internal coal fire which ignited the magazines. This was a likely cause of the explosion, rather than the initial hypothesis of a mine
 
        
                    
             
        
        
        
American Indian tribes were no longer recognized. The answer is D
        
                    
             
        
        
        
The main way in which the nature of European exploration changed by the seventeenth century was that by this time, the major European powers such as Spain and Portugal had claimed large amounts of territory in the New World, and already exporting large amounts of natural resources back to their homeland. 
        
             
        
        
        
     The first crop that formed the basis of the economy in the Southern states was tobacco. But at the beginning of the 19th century cotton became the most important. During the 1840s and 1850s cotton became the chief United States export. It was known as "King cotton". The rapid agricultural growth of the South led to financial and political tensions between the Northern and the Southern states.  Answer: The most important Southern crop in the 1840s and 1850s was cotton.