What factors old and new led to the widespread outbreak of revolutions in 1848? were the cause in the various countries essentially the same, or did each have its own particular set of circumstances? why did these revolutions fail throughout europe? what roles did liberals and nationalists play in the revolutions? why did they sometimes clash?

The revolutions across Europe in 1848 were the result of several factors.  In 1815, the Congress of Vienna redrew the map of Europe following the Napoleonic Wars.  The leaders that made the decisions in Vienna were conservatives and reactionaries (wanting to return things to the old way).  Initially, the French Revolution had been inspired by liberal and democratic ideas.  The Congress of Vienna negated much of that progress.  Liberals and nationalists were often at odds with each other because some groups wanted to reform the existing political systems, while others wanted to overthrow the government.    
  
The meeting at Vienna had also reinstated the monarchy in France, and wealthy, conservative nobles aimed to restore the old order that existed prior to the French Revolution.  In France, this anger was demonstrated in 1830, against King Charles X and again in 1848 during the reign of Louis Philippe.  In France, the 1848 revolution ended as the rebels declared France to be a republic, but it would not last long.    

Inspired by events in France, liberal revolutionaries in other European countries began to fight for greater political rights.  Frustration in countries such as Austria, Prussia, and Italy were significant and led to multiple uprisings and revolutions in 1848.  (See image:  Courtesy of Wikipedia) In Italy, the goal of political revolution was to transform the peninsula into a nation-state by unifying the different regions.  Inspired by Giuseppe Mazzini, this was accomplished.  And yet, the result of this upheaval was the establishment of a monarchy.  Distinct cultural and economic divisions within Italy still remained as well. 

In Austria and Prussia, much revolutionary activity had been suppressed by the government since 1815.  In Vienna 1848, nationalist groups began to demand freedoms such as speech and press and representative government.  But, disagreements between nationalists groups and more radical factions allowed conservatives to maintain control in Austria.  In the German states, Prussia was the largest and most influential economic power.  Efforts to unified Germany as a nation were hampered by Prussia's king attempting to maintain their own political and economic sovereignty.  Nationalist revolutions in Frankfurt and Berlin demonstrated that not all Germans agreed with this approach.  It should also be noted that The Communist Manifesto by Karl Marx was published in Germany in 1848, adding a new dimension to and inspiration for ideological debate.   

In the end, these political revolutions had mixed results.  The year 1848 led to the frustration and discontent of many working class citizens and only partially successful experiments with republican and eventually socialist governments.  Despite the uprisings, the political status quo was more or less maintained.     

Yes, reasons why is sectionalism compromise of 1850 and secession i hope this