Federal systems divide authority between a central government and constituent units, and how that division works determines much of what is politically possible.
The allocation
Constitutions typically enumerate powers of the central government and reserve the remainder, or the reverse.
Which produces different defaults — a system reserving unenumerated powers to the units differs from one reserving them centrally.
Concurrent powers, exercised by both levels, exist in most systems and are where conflict concentrates.
Supremacy
Where laws conflict, most federal systems provide that central law prevails within its sphere.
Which makes the scope of that sphere the central question, and it has been litigated continuously in every federal system.
Preemption — central law displacing unit law in a field — can be explicit or implied, and implied preemption generates substantial litigation.
Fiscal federalism
Where the practical power frequently lies.
Central governments generally raise more revenue than they spend directly, and units spend more than they raise.
Which creates transfers, and conditions attached to transfers allow central influence over areas outside central legislative authority.
Conditional funding is therefore a mechanism for central policy in fields constitutionally reserved to units, and its limits have been litigated.
Variation between units
Federal systems produce different policies in different places by design.
Which allows experimentation, with successful approaches spreading, and is frequently described as laboratories of policy.
Evidence for policy diffusion between units is substantial in comparative research.
It also produces inequality in provision, which is the corresponding criticism.
The race to the bottom question
Whether competition between units drives standards down, as units compete for business by reducing regulation and taxation.
Evidence is mixed and varies by policy area, with stronger support for tax competition than for environmental or labour standards generally.
Which means the concern is real in some domains and overstated as a general proposition.
Local government
A third level in most systems, with authority derived from the unit rather than constitutionally protected in many cases.
Which means local powers can be removed by the level above, and preemption of local ordinances by state or provincial governments has become a significant pattern in several countries.
Cities frequently attempt policy that higher levels then prohibit, which is a recurring dynamic.
Emergency powers
Divisions of authority are tested during emergencies, where central coordination and local implementation must interact.
Which produced substantial friction in several countries during recent public health emergencies, with authority disputes affecting response.
Emergency frameworks specifying who decides what, agreed in advance, work better than negotiation during a crisis.
Why the boundaries move
Interpretation shifts with courts, with political circumstances and with practical necessity.
Which means the formal constitutional text describes a framework within which the actual balance has shifted substantially over time in every federal system.
Tracking that shift requires reading the litigation rather than the constitution.
Intergovernmental machinery
Formal bodies where levels of government coordinate.
Which exist in most federal systems with varying authority, from consultative to decision-making.
Where they work well, they resolve disputes without litigation, which is faster and less adversarial.
Asymmetric federalism
Where different units have different powers.
Which exists in several systems, generally reflecting historical settlements with particular regions.
It accommodates genuine differences and generates arguments about equality between units.
Secession and territorial questions
Constitutions differ in whether they address it, with most silent or prohibitive.
Which has produced constitutional crises where independence movements have sought referendums.
Judicial rulings in some systems have set out frameworks requiring negotiation following a clear expression of will, without recognising a unilateral right.
Fiscal equalisation
Transfers between units to reduce disparities in fiscal capacity.
Which exist in most federal systems with different formulas and different degrees of equalisation.
They are politically contentious, since wealthier units fund them, and the formulas are periodically renegotiated.
Regulatory competition and harmonisation
Businesses operating across units face multiple regimes, which creates pressure for harmonisation.
Which can occur through central legislation, through mutual recognition, or through units voluntarily adopting model laws.
The choice between them determines who sets the standard.
Where to look
Constitutional court decisions on the division of powers are the primary record of where the boundary currently sits.
Which shifts over time, and reading recent rulings gives a more accurate picture than the constitutional text alone.
Public understanding
Surveys frequently find confusion about which level of government is responsible for what.
Which affects accountability directly, since voters cannot hold the right body responsible if they do not know which it is.
Clear allocation and clear communication of it are therefore accountability mechanisms rather than administrative details.
Comparative variation
Federal systems differ enormously in how centralised they are in practice, independently of formal constitutional allocation.
Which is measured by fiscal shares, regulatory authority and policy variation between units.
Some formally federal systems are more centralised in practice than some formally unitary ones with strong devolution.