Explain how Spain's economy became weak over time. Use details to support your answer.

The main cause of Spain's crisis was the housing bubble and the accompanying unsustainably high GDP growth rate. The ballooning tax revenues from the booming property investment and construction sectors kept the Spanish government's revenue in surplus, despite strong increases in expenditure, until 2007.  

The inflation or increase of taxes, spain exporting goods to other countries which made spain's enemies rich, and the dutch revolt weakened spain.

answer; (a) he was a u.s senator for 38 years;

i believe it would influence their own way of understanding things. it shall be a foundation where they can draw or start an argument.   historians are also  scientists that  have their tools of analysis and expertise to unlock a variety of difficulties such as relationships of man, origin, politics, economy, and culture. based on facts and understanding on these areas, they may shade light to extract ideas and develop options to validate a hypothesis or debunk it.