The categories are political, social and economic reason for migration.
List of Reasons: 
• Ireland’s potato crop failed - economic.
• “Poor law” taxed Ireland’s small farmers. - political.
• New factories in Germany put people out of work - economic. 
• A freedom revolution in Germany failed - political. 
• Few jobs existed for workers in China - economic. 
• People in some foreign nations were persecuted for their beliefs - political. 
• People searched for adventure - social. 
• A rumor spread in Germany that America would stop immigration - social.